Copy-forgery-inhibited pattern image generation method and image processing apparatus

ABSTRACT

A combination of a latent-image pattern which forms a latent-image part and a background pattern that forms a background-image part is determined so that the latent-image part and background-image part have equal print densities. The determined latent-image pattern and background pattern, color information used to determine a color of the copy-forgery-inhibited pattern image, input image information as an image to be processed, copy-forgery-inhibited pattern basic information used to designate the latent-image part and background-image part, and camouflage region designation image information used to designate a camouflage region are input. A copy-forgery-inhibited pattern image is generated on the basis of the input information.

FIELD OF THE INVENTION

The present invention relates to a technique for compositing acopy-forgery-inhibited pattern on the background of a document, andoutputting a composite document for the purpose of deterring illicitforgery and information leakage due to copies of important documents.

BACKGROUND OF THE INVENTION

On some receipts, securities, and certificates, a special pattern whichemerges as a character string or image when they are copied is printedon the background, so as to prevent them from being readily copied. Suchspecial pattern is generally called a “copy-forgery-inhibited pattern”,which applies a mechanism that does not allow an original to be readilycopied, thus psychologically deterring a copy of an original.

This copy-forgery-inhibited pattern is formed of two regions having anidentical density, i.e., a region where dots remain after copying and aregion where dots disappear after copying. These two regions havesubstantially the same densities, and a hidden character string or imagesuch as “COPY” cannot be seemingly recognized macroscopically, but theseregions microscopically have different properties. Note that the hiddencharacter string or image will be referred to as a “latent-image”hereinafter.

For example, the region where dots remain after copying (this regionwill be referred to as a latent-image part or region hereinafter) isformed of groups of dots where dots are concentrated, and the regionwhere dots disappear or become lighter than the latent-image part aftercopying (this region will be referred to as a background-image part orregion hereinafter) is formed of scattered dots. In this manner, the tworegions which have substantially the same densities but differentproperties can be created.

The concentrated dots and scattered dots can be generated by halftoningusing halftone dot screens with different screen ruling values ordithering using dither matrices having different features as an imageprocess.

In halftoning, a halftone dot screen with a low screen ruling value ispreferably used to obtain the concentrated dot layout, and a halftonedot screen with a high screen ruling value is preferably used to obtainthe scattered dot layout.

In the dithering using a dither matrix, a dot-concentration dithermatrix is preferably used to obtain the concentrated dot layout, and adot-scattering dither matrix is preferably used to obtain the scattereddot layout.

Therefore, when a copy-forgery-inhibited pattern image is generatedusing the aforementioned halftoning, halftoning with a low screen rulingvalue is suited to a latent-image part, and halftoning with a highscreen ruling value is suited to a background-image part. When acopy-forgery-inhibited pattern image is generated using theaforementioned dithering, dithering using a dot-concentration dithermatrix is suited to a latent-image part, and dithering using adot-scattering dither matrix is suited to a background-image part.

In general, a copying machine suffers a limitation on image reproductionperformance depending on the input resolution upon reading small dots ofa document to be copied or the output resolution upon reproducing smalldots. Therefore, when a document includes isolated small dots beyond thelimitation on the image reproduction performance of the copying machine,these small dots cannot be perfectly reproduced on its copy, and theisolated small dots disappear.

That is, when the background-image part which forms thecopy-forgery-inhibited pattern image is designed to exceed thelimitation of dots that can be reproduced by the copying machine, largedots (concentrated dots) of the copy-forgery-inhibited pattern can bereproduced by copying, but small dots (scattered dots) cannot bereproduced. Hence, a hidden image (latent-image) emerges. Also, evenwhen scattered dots do not completely disappear after copying, if theyhave an apparent density difference from-concentrated dots aftercopying, a hidden image (latent-image) emerges.

In the copy-forgery-inhibited pattern, a technique called “camouflage”which makes it harder to recognize a hidden character string or image asa latent-image is well known. This camouflage technique is a method oflaying out a pattern which has a density different from that of thelatent-image part and background-image part on the entirecopy-forgery-inhibited pattern image. This technique has an effect ofmacroscopically emphasizing the camouflage pattern with a densitydifferent from that of the latent-image part and background-image part,and further obscuring a latent-image at a glance.

The copy-forgery-inhibited pattern with the camouflage pattern has aneffect of giving a decorative impression to a print compared to acopy-forgery-inhibited pattern without any camouflage pattern. Dotsinside the camouflage pattern preferably disappear as much as possibleso as to allow easy recognition of a latent-image after copying. In caseof the simplest implementation, camouflage can be realized by printingno dots at positions corresponding to the camouflage pattern.

An overview of the copy-forgery-inhibited pattern has been explained.

Conventionally, a print paper vendor prints-a copy-forgery-inhibitedpattern including a character string or image (latent-image) such as“COPY” or the like on dedicated sheets, and sells such sheets ascopy-inhibition paper sheets. The government and other public offices,and companies buy such copy-inhibition paper sheets, and print documentswhose authenticity is to be guaranteed on copy-inhibition paper sheets,thus deterring copies of prints.

Since the aforementioned copy-inhibition paper sheets are marketed aspre-print sheets by pre-printing a copy-forgery-inhibited pattern imageon dedicated sheets by a print paper vendor, users have demerits interms of cost such as cost produced upon using dedicated sheets, costproduced upon preparing pre-print sheets more than necessary, and thelike.

By contrast, in recent years, a technique for creating acopy-forgery-inhibited pattern image by software, and outputting acomposite document of that copy-forgery-inhibited pattern image andcontents image using a laser printer (to be referred to as “on-demandcopy-forgery-inhibited pattern output method by printer” hereinafter)has been realized (e.g., see patent reference 1: Japanese PatentLaid-Open No. 2001-197297).

With this on-demand copy-forgery-inhibited pattern output method by aprinter, since a document with a copy-forgery-inhibited pattern imagecan be printed using plain paper, only a required number of documentswith a copy-forgery-inhibited pattern image on their backgrounds can beprinted when needed. Therefore, copy-inhibition paper sheets need not beprepared more than necessary unlike in the conventional method. That is,the on-demand copy-forgery-inhibited pattern output method by a printercan greatly reduce cost of sheets compared to the conventional documentcopy-deterrence method using copy-inhibition paper sheets.

The user of the conventional copy-inhibition paper sheets can use only acharacter string or image (latent-image) prepared in advance by theprint paper vendor or a made-to-order hidden character string or image(latent-image).

However, with the on-demand copy-forgery-inhibited pattern output methodby a printer, the user can generate a copy-forgery-inhibited patternimage including an arbitrary hidden character string or image(latent-image) by a software process for each print, and can print iton-demand using a printer. Hence, the user can freely customize a hiddencharacter string or image (latent-image).

By exploiting a merit of on-demand selection of a latent-image, not onlya corporation logo mark or a character string “VOID”, which is usedconventionally, but also various kinds of information such as a serialnumber or IP address used to identify an output printer, a computer nameor IP address used to identify a computer that issues a print command, auser name or login name used to identify a user who issues a printcommand, a print job number, print date, print location, the file nameof a digital document, and the like used to identify when and by whom aprint process is done, and so forth can be selected as an image orcharacter string to be embedded as a latent-image.

As a result, the on-demand copy-forgery-inhibited pattern output methodby a printer can implement an advanced tracking function that cannot beimplemented by the conventional pre-printed copy-inhibition papersheets.

In the on-demand copy-forgery-inhibited pattern output method by aprinter, the generation timing of a copy-forgery-inhibited pattern imageis processed mainly using a personal computer (PC) or workstation, and aprinter controller for some processes. However, computers and printersinclude various models, i.e., from a model having high computationperformance and a sufficiently large memory size to a model having poorcomputation performance and a small memory size.

Even if a computer and printer have sufficiently high performance,assuming that a high-resolution copy-forgery-inhibited pattern image isto be generated in large quantities, the computation volume and memorysize required to generate a copy-forgery-inhibited pattern image arepreferably reduced as much as possible.

Patent reference 1 that describes the on-demand copy-forgery-inhibitedpattern output method by a printer also describes a method of reducingthe computation volume and memory size upon generation of acopy-forgery-inhibited pattern image. However, patent reference 1 canachieve reductions of the computation volume and memory size in someprocesses, but cannot achieve both reductions of the computation volumeand memory size and high image quality.

For example, patent reference 1 describes a method of executing aprocess for separating a color main image as contents such as a documentor the like into color components such as Y, M, C, and K or the like,and compositing a copy-forgery-inhibited pattern image as a monochromeimage in a designated color component of the main image upon compositingthe main image and copy-forgery-inhibited pattern image.

However, for example, if a color component in which thecopy-forgery-inhibited pattern image is to be embedded is C (cyan) andthe copy-forgery-inhibited pattern image is to be composited to the Ccomponent of the color main image, only when other color components ofthe color main image are zero, the color of the color main imagecomposited with the copy-forgery-inhibited pattern image is output ascyan. Otherwise, cyan is mixed with other color components and amixed-color copy-forgery-inhibited pattern may be output (for example,mixing of cyan and yellow generates green).

Patent reference 1 does not describe any method of compositing acopy-forgery-inhibited pattern image in an accurate color to only adesignated region (coordinate position, color component) of an inputimage.

In patent reference 1, a camouflage pattern and background image areintegrated in advance, and error diffusion is applied to the integratedbackground image with the camouflage pattern to generate a binarizedbackground image. However, the camouflage pattern in the backgroundimage binarized by error diffusion may suffer positional deviation fromthat in a multi-valued background image.

Error diffusion is a method of ON/OFF of a dot by comparing the sum ofthe pixel value of a pixel to be binarized and errors distributed fromsurrounding pixels to that pixel value with a predetermined thresholdvalue. However, error diffusion suffers known problems, e.g., “delay ofdot generation” (errors are sufficiently accumulated in black dotgeneration at the leading end of a low-density region or white dotgeneration at the leading end of a high-density region and dotgeneration delays considerably until dots are fixed down to a steadystate), “excessive diffusion” (errors accumulated in large quantitiesare diffused to outside a region), and the like.

Therefore, even when error diffusion is applied to a background imagewith a camouflage pattern to generate a binary background image with acamouflage pattern, “delay of dot generation” and “excessive diffusion”may occur in pixels around the camouflage pattern.

When halftoning is applied to a latent-image part designated by a maskimage, e.g., ON/OFF of a dot is determined by comparing the pixel valueof a background image and a threshold matrix value, “delay of dotgeneration” and “excessive diffusion” as problems of error diffusion donot occur.

Therefore, a camouflage pattern obtained as a result of error diffusionmay not match that as a result of halftoning at their boundaries.

Patent reference 1 also describes a method of applying halftoning to alatent-image part to binarize it, and binarizing the entire backgroundimage including the latent-image part by error diffusion. However, inthis case, dots generated by error diffusion get into the latent-imageregion to disturb the boundary between the latent-image region andbackground region, thus impairing the quality of thecopy-forgery-inhibited pattern image.

Therefore, the conventional method does not sufficiently consider anyefficient computation volume/memory size reduction method upongeneration of a copy-forgery-inhibited pattern image while maintaininghigh image quality of the copy-forgery-inhibited pattern image.

As described above, many efforts have been made in thecopy-forgery-inhibited pattern to make it harder to recognize alatent-image. The camouflage technique is one of such efforts.

However, the on-demand copy-forgery-inhibited pattern output method by aprinter is susceptible to density variations of a printer. In additionto the camouflage technique, efforts that make it harder to recognize alatent-image are required even when the density variations of a printerhave occurred.

SUMMARY OF THE INVENTION

The present invention has been made to solve the aforementionedproblems, and has as its object to achieve high-speed, memory-savinggeneration of a copy-forgery-inhibited pattern image under theassumption that a copy-forgery-inhibited pattern image is generated inenvironments using various computers and printers.

It is another object of the present invention to provide an adequatelycamouflaged copy-forgery-inhibited pattern image free from anydisturbance, which cannot be obtained by the prior art.

It is still another object of the present invention to generate acopy-forgery-inhibited pattern image that can make harder to recognize alatent-image.

In order to achieve the above objects, according to one aspect of thepresent invention, there is provided a copy-forgery-inhibited patternimage generation method in an image processing apparatus for generatinga copy-forgery-inhibited pattern image including a latent-image part andbackground-image part, comprising:

a step of determining a combination of a latent-image pattern whichforms the latent-image part and a background pattern that forms thebackground-image part so that the latent-image part and background-imagepart have equal print densities;

a step of inputting the determined latent-image pattern and backgroundpattern, color information used to determine a color of thecopy-forgery-inhibited pattern image, input image information as animage to be processed, copy-forgery-inhibited pattern basic informationused to designate the latent-image part and background-image part, andcamouflage region designation image information used to designate acamouflage region; and

a step of generating the copy-forgery-inhibited pattern image on thebasis of the input information.

According to one aspect of the present invention, there is provided acopy-forgery-inhibited pattern image generation method for generating acopy-forgery-inhibited pattern image including a latent-image part whichis reproduced upon copying, and a background-image part which disappearsupon copying, comprising:

dividing the latent-image part into a plurality of regions; and

controlling a dot layout to lay out dots which are reproduced uponcopying on at least one region of the plurality of regions, and not tolay out the dots on at least one region different from the at least oneregion.

According to one aspect of the present invention, there is provided animage processing apparatus for generating a copy-forgery-inhibitedpattern image including a latent-image part and background-image part,comprising:

means for determining a combination of a latent-image pattern whichforms the latent-image part and a background pattern that forms thebackground-image part so that the latent-image part and background-imagepart have equal print densities;

means for inputting the determined latent-image pattern and backgroundpattern, color information used to determine a color of thecopy-forgery-inhibited pattern image, input image information as animage to be processed, copy-forgery-inhibited pattern basic informationused to designate the latent-image part and background-image part, andcamouflage region designation image information used to designate acamouflage region; and

means for generating the copy-forgery-inhibited pattern image on thebasis of the input information.

According to one aspect of the present invention, there is provided animage processing apparatus for generating a copy-forgery-inhibitedpattern image including a latent-image part which is reproduced uponcopying, and a background-image part which disappears upon copying,comprising:

control means for dividing the latent-image part into a plurality ofregions, and controlling a dot layout to lay out dots which arereproduced upon copying on at least one region of the plurality ofregions, and not to lay out the dots on at least one region differentfrom the at least one region.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the internal process of acopy-forgery-inhibited pattern compositing/printing apparatus accordingto the first embodiment;

FIG. 2 is a flowchart showing the internal processing sequence of acopy-forgery-inhibited pattern image generation unit 101 in the firstembodiment;

FIG. 3 shows an example of a 4×4 spiral dither matrix;

FIG. 4 shows threshold patterns (dot layouts) obtained by applying athreshold process to predetermined input image signals using the 4×4screw dither matrix shown in FIG. 3;

FIG. 5 shows an example of a 4×4 Bayer dither matrix;

FIG. 6 shows threshold patterns (dot layouts) obtained by applying athreshold process to predetermined input image signals using the 4×4Bayer dither matrix shown in FIG. 5;

FIG. 7 is a view for comparing the area ratios of a background thresholdpattern and latent-image threshold pattern;

FIG. 8 shows graphs showing the relationships between the area ratios ofblack pixels of threshold patterns obtained by applying a thresholdprocess to input image signals using a dither matrix, and the densitiesupon printing the threshold patterns;

FIG. 9 is a view showing the generation process of acopy-forgery-inhibited pattern image using a copy-forgery-inhibitedpattern compositing/printing apparatus shown in FIG. 1;

FIG. 10 show examples of a copy-forgery-inhibited pattern basic image115 and camouflage region designation image 117;

FIG. 11 shows examples of a latent-image threshold pattern 114 andbackground threshold pattern 116;

FIG. 12A partially shows a copy-forgery-inhibited pattern imagegenerated by the copy-forgery-inhibited pattern image generation unit101 by a boundary process;

FIG. 12B shows an example of a copy-forgery-inhibited pattern image witha checkered pattern layout;

FIG. 12C shows an example of a copy-forgery-inhibited pattern image witha checkered pattern type crossover layout;

FIG. 12D is an enlarged view of a region designated by acopy-forgery-inhibited pattern basic image shown in FIG. 12C;

FIG. 13 is a view showing a composition process of an input documentimage and copy-forgery-inhibited pattern image;

FIG. 14 is a view showing a method of compositing acopy-forgery-inhibited pattern image to an input document image to whichvarious images have already been composited and which has no layerstructure;

FIG. 15 is a block diagram showing the internal arrangement of acopy-forgery-inhibited pattern compositing/printing apparatus forcompositing a copy-forgery-inhibited pattern image to an input documentimage to which various images have already been composited and which hasno layer structure;

FIG. 16 shows a latent-image threshold pattern and background thresholdpatterns obtained by applying a threshold process to the gray levels ofa plurality of input image signals using a dither matrix;

FIG. 17 shows an example of a test print sheet on which patches aretwo-dimensionally laid out by changing the densities of background-imageand latent-image parts;

FIG. 18 is a flowchart showing the simplest test print sequence;

FIG. 19 is a flowchart of a test printing process with a reinforceddensity adjustment function compared to the test printing process shownin the flowchart of FIG. 18;

FIG. 20 shows two different types of sheets used in the test printingprocess, the processing sequence of which is shown in FIG. 19;

FIG. 21 is a flowchart showing the processing sequence of a multi-steptest printing process with an advanced function;

FIG. 22 is a block diagram showing the internal arrangement of anapparatus which executes a copy-forgery-inhibited pattern test printingprocess;

FIG. 23 is a block diagram showing a copy-forgery-inhibited patterncompositing/printing apparatus with a copy-forgery-inhibited patterndensity calibration function;

FIG. 24 shows a modification of a test print sheet explained in thefirst embodiment; and

FIG. 25 is a block diagram showing the basic arrangement of a computerin the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The best mode of carrying out the invention will be described in detailhereinafter with reference to the accompanying drawings. In thisembodiment, an image corresponding to a background-image part isdesigned to discretely lay out dots using a dot-scattering dithermatrix, and an image corresponding to a latent-image part is designed toconcentratedly lay out dots using a dot-concentration dither matrix.

The background-image part will be explained as a “region whichdisappears” upon copying for the descriptive convenience of the presentinvention. However, the present invention is not limited to this. Forexample, the background-image part may be printed to have a lowerdensity than the latent-image part, so that when a print formed with acopy-forgery-inhibited pattern image is copied by a copying machine, aperson can recognize that the obtained copy is not an original (theprint formed with the copy-forgery-inhibited pattern image) by thevisualized latent-image part. That is, an image of the background-imagepart need not “disappear” from the copy, and need only have a densitylevel that allows the user to identify the latent-image part.

A dither matrix used to generate an image of the background-image partwill be referred to as a background dither matrix hereinafter, and adither matrix used to generate an image of the latent-image part will bereferred to as a latent-image dither matrix hereinafter.

Dithering is a method of comparing a multi-valued input image signalwith a threshold value calculated according to a given rule, andoutputting a binary image based on their magnitude relationship. Adither matrix is a threshold matrix in which threshold values used tobinarize an input image signal by dithering are two-dimensionally laidout.

By binarizing the pixel values of an input image signal by correspondingthreshold values of the dither matrix, a binary image (thresholdpattern) is obtained. In the binary image to be obtained, when the graylevel of the input image signal is less than a threshold value of thedither matrix, one bit (e.g., 1) is assigned to the pixel value; whenthe gray level is equal to or larger than the threshold value, the otherbit (e.g., 0) is assigned.

In this embodiment, a binary image which forms the background-imagepart, and a binary image which forms the latent-image part are generatedin advance by dithering by inputting appropriate input image signals, sothat the background-image part and latent-image part have substantiallythe same densities when they are printed on a paper sheet using aprinter.

A method of generating a background threshold pattern and latent-imagethreshold pattern, which can set the background-image part andlatent-image part to have substantially the same densities upon printingon a paper sheet using a printer will be described in detail later.

In the following description, a binary image that forms thebackground-image part will be referred to as a background thresholdpattern, and a binary image that forms the latent-image part will bereferred to as a latent-image threshold pattern.

First Embodiment

In this embodiment, a combination of a background threshold pattern andlatent-image threshold pattern as patterns (binary images) which formthe background-image part and latent-image part and can set equaldensities for the background-image part and latent-image part uponprinting is determined in advance, and logical operations are executedusing the background threshold pattern, the latent-image thresholdpattern, a copy-forgery-inhibited pattern basic image as a binary imagethat designates the latent-image part and background-image part, and acamouflage region designation image as a binary image that designates acamouflage region, thereby generating a copy-forgery-inhibited patternimage at high speed using a small memory size.

Note that the background threshold pattern and latent-image thresholdpattern are parameters that determine the densities of thebackground-image part and latent-image part of a copy-forgery-inhibitedpattern image upon printing, and are practical elements of“copy-forgery-inhibited pattern density parameters”.

Since a copy-forgery-inhibited pattern image is generated by executinglogical operations for determining ON/OFF of dots of thecopy-forgery-inhibited pattern image for each pixel, the memory sizerequired to generate the copy-forgery-inhibited pattern image is greatlyreduced.

FIG. 1 is a block diagram showing the internal process of acopy-forgery-inhibited pattern compositing/printing apparatus of thefirst embodiment. This copy-forgery-inhibited patterncompositing/printing apparatus comprises a copy-forgery-inhibitedpattern image generation unit 101, composition unit 102, print dataprocessing unit 103, and print unit 104. In this embodiment, thecopy-forgery-inhibited pattern compositing/printing apparatus will beexplained as a device including the aforementioned units. However, thepresent invention is not limited to such specific arrangement. Forexample, the copy-forgery-inhibited pattern compositing/printingapparatus may be configured as a system in which thecopy-forgery-inhibited pattern image generation unit 101, compositionunit 102, and print data processing unit 103 are implemented by a singledevice such as a computer or the like, and a printing device which cancommunicate with this computer has the print unit 104.

The copy-forgery-inhibited pattern image generation unit 101 receives aninput background-image 112, color information 111, processing regioninformation 113, latent-image threshold pattern 114, backgroundthreshold pattern 116, copy-forgery-inhibited pattern basic image 115,and camouflage region designation image 117, and generates and outputs acopy-forgery-inhibited pattern image 118. The copy-forgery-inhibitedpattern image generation unit 101 generates the copy-forgery-inhibitedpattern image 118 by applying image processes to the input backgroundimage 112 according to predetermined rules. Note that the inputbackground image 112 can be either a multi-valued image or binary image.The processing region information 113 indicates a region which is toundergo a copy-forgery-inhibited pattern embedding process in inputimage information.

The copy-forgery-inhibited pattern basic image 115 is used to designateminimum elements including the latent-image part and background-imagepart, and is made up of 1 bit per pixel. One bit (e.g., 1) of thecopy-forgery-inhibited pattern basic image 115 designates thelatent-image part, and the other bit (e.g., 0) designates thebackground-image part. The camouflage region designation image 117 isused to designate a region where a lower density is to be set so as toprovide a camouflage effect, and is made up of 1 bit per pixel as in thecopy-forgery-inhibited pattern basic image 115. One bit (e.g., 1) of thecamouflage region designation image 117 designates a non-camouflageregion, and the other bit (e.g., 0) designates a camouflage region wherea lower density is to be set compared to the surrounding portion.

FIG. 10 shows examples of the copy-forgery-inhibited pattern basic image115 and camouflage region designation image 117. Referring to FIG. 10,reference numeral 1001 denotes an example of the copy-forgery-inhibitedpattern basic image 115. Reference numeral 1002 denotes an example ofthe camouflage region designation image 117.

As has already been described above, the background threshold pattern116 and latent-image threshold pattern 114 are generated by applyingthreshold processes using the threshold values of the background andlatent-image dither matrices to appropriate image signals, so that thesepatterns are to be output to have an equal density when they are printedout.

FIG. 11 shows examples of the latent-image threshold pattern 114 andbackground threshold pattern 116. Referring to FIG. 11, referencenumeral 1101 denotes a latent-image threshold pattern; and 1102, abackground threshold pattern.

The copy-forgery-inhibited pattern image 118 generated by thecopy-forgery-inhibited pattern image generation unit 101 is output tothe composition unit 102. The generation method of thecopy-forgery-inhibited pattern image 118 will be described in detaillater.

The composition unit 102 generates a copy-forgery-inhibited patterncomposited output document image by compositing the input document image119 and the generated copy-forgery-inhibited pattern image 118. When thecopy-forgery-inhibited pattern image 118 is directly output as acopy-forgery-inhibited pattern composited output document imageirrespective of the contents of the input document image 119, thecomposition unit 102 need not refer to the input document image 119. Atthis time, the copy-forgery-inhibited pattern image 118 and objectswhich form the input document image 119 may undergo a color matchingprocess, and the objects which form the input document image 119 may becomposited to the copy-forgery-inhibited pattern image 118 to generatethe copy-forgery-inhibited pattern composited output document image.Alternatively, the next print data processing unit 103 may apply a colormatching process to the copy-forgery-inhibited pattern composited outputdocument image.

The print data processing unit 103 receives the copy-forgery-inhibitedpattern composited output document image composited by the compositionunit 102 as rendering information via a rendering interface of an OS(operating system) (e.g., Graphic Device Interface (GDI) of Windows®series of Microsoft Corporation, QuickDraw of MacOS series as an OS ofApple Computer, Inc., and the like are well known), and sequentiallyconverts it into a print command. At this time, image processes such asa color matching process, RGB-CMYK conversion, halftone process, and thelike are executed as needed. The print data processing unit 103 sends,as the copy-forgery-inhibited pattern composited output document imagedata, a data format that can be interpreted by the print unit 104 (e.g.,a data format described in a page description language, or a data formatrasterized to a print bitmap) to the next print unit 104.

The print unit 104 prints out a copy-forgery-inhibited patterncomposited output document image in accordance with information of theinput copy-forgery-inhibited pattern composited output document imagedata. A laser beam printer will be exemplified below. The print unit 104comprises a printer controller and printer engine (not shown). Thisprinter controller comprises a print information control unit, pagememory, output control unit, and the like. The print information controlunit interprets a page description language (PDL) sent from the printdata processing unit 103, and rasterizes patterns corresponding torendering and printing commands on the page memory.

In this case, image processes such as RGB-CMYK conversion, a halftoneprocess, and the like are executed as needed. When a print bitmap isdetermined in place of the data format described in the page descriptionlanguage, image data is directly rasterized on the page memory.

The output control unit converts the contents of the page memory into avideo signal, and outputs it to the printer engine. This printer enginecomprises, e.g., a print medium convey mechanism, semiconductor laserunit, photosensitive drum, developing unit, fixing unit, drum cleaningunit, separation unit, and the like, and prints using a knownelectrophotography process.

When the copy-forgery-inhibited pattern image generation unit 101generates a copy-forgery-inhibited pattern image which is designed tooutput respective pixels using only a primary color (cyan, yellow,magenta, or black) of the printer, it is not desirable that respectivepixels which are expressed to be output using the primary color (cyan,yellow, magenta, or black) of the printer are printed using a pluralityof different colors of inks or toners. Therefore, the print dataprocessing unit 103 and print unit 104 are preferably set not tosimultaneously express pixel values (e.g., cyan, magenta, yellow, orblack) corresponding to the copy-forgery-inhibited pattern image in thecopy-forgery-inhibited pattern composited output document image using aplurality of different colors of inks or toners, i.e., a mixed color.

More specifically, a setup that prints a copy-forgery-inhibited patternimage always using a monochrome ink or toner even after a colorconversion process such as color matching or the like is skipped and ahalftone process is executed is preferably introduced. However, this isnot the case when one pixel of the copy-forgery-inhibited pattern imageis expressed by light and dark inks or large and small ink dots of anidentical color by an ink-jet printer. As color variations of acopy-forgery-inhibited pattern image, a copy-forgery-inhibited patternimage which looks green may be generated by laying out cyan and yellowpixels in a balanced manner. In this case as well, if one pixel of thecopy-forgery-inhibited pattern image is formed of the primary color(cyan, yellow, magenta, or black) of the printer, it is preferablyaccurately output using only a corresponding cyan or yellow toner orink.

However, an image that can implement a copy-forgery-inhibited patterneffect can be generated without printing out one pixel of thecopy-forgery-inhibited pattern image using only the primary color (cyan,yellow, magenta, or black) of the printer. Even when one pixel of thecopy-forgery-inhibited pattern image is expressed by a plurality ofdifferent colors of inks or toners, such copy-forgery-inhibited patternimage can be used as a copy-forgery-inhibited pattern as long as alatent-image remains after copying.

In this embodiment, assume that all of the copy-forgery-inhibitedpattern image, input document image, copy-forgery-inhibited patterncomposited output document image, and copy-forgery-inhibited patterncomposited output document image data are digital data, and acopy-forgery-inhibited pattern composited output document represents animage printed on a paper sheet.

The internal process of a copy-forgery-inhibited pattern generationapparatus will be described below using FIG. 2.

FIG. 2 is a flowchart showing the internal processing sequence of thecopy-forgery-inhibited pattern image generation unit 101 in the firstembodiment. In step S201, a copy-forgery-inhibited pattern imagegeneration process starts via a user interface or the like. In stepS202, the input background image 112, background threshold pattern 116,latent-image threshold pattern 114, copy-forgery-inhibited pattern basicimage 115, and camouflage region designation image 117 are loaded.

In step S203, an initial pixel upon generation of acopy-forgery-inhibited pattern image is determined. For example, whenthe entire input image undergoes an image process in the raster scanorder from the upper left position to the lower right position to beconverted into a copy-forgery-inhibited pattern image, the upper leftposition is set as an initial position.

In step S204, the background threshold pattern 116, latent-imagethreshold pattern 114, copy-forgery-inhibited pattern basic image 115,and camouflage region designation image 117 are to be laid out in a tilepattern from the upper left position, and equation (1) given by:

$\begin{matrix}{{nWriteDotOn} = {{nCamouflage}\; \times \left( {{{nSmallDotOn}\; \times \overset{\_}{nHiddenMark}}\; + {{nLargeDotOn}\; \times {nHiddenMark}}} \right)}} & (1)\end{matrix}$where

nCamouflage: 0 if a pixel of interest in the camouflage regiondesignation image is a pixel which forms a camouflage pattern;otherwise, 1

nSmallDotOn: 1 if the pixel value of the background threshold pattern isblack; 0 if it is white (the colors are not limited to these specificcolors)

nLargeDotOn: 1 if a pixel value of the latent-image threshold pattern isblack; 0 if it is white (the colors are not limited to these specificcolors)

nHiddenMark: 1 if a pixel of interest in the copy-forgery-inhibitedpattern basic image is a pixel which forms a latent image; 0 if it is apixel that forms a background image

/nHiddenMark: NOT of nHiddenMark. It assumes 0 for the latent-imagepart; 1 for the background-image part.

is calculated for a pixel to be processed of the input background image112 to check if a corresponding pixel value is to be written in a dotupon printing. At this time, a pixel value corresponds to the inputcolor information 111.

Note that whether or not a corresponding pixel value is to be written ina dot upon printing may be determined with reference to the pixel valueof the input background image at that time. In this case, a term(nBackground) obtained with reference to the input background-image maybe multiplied by the right-handed side of equation (1). This nBackgroundassumes 1 if the input background image corresponds to a region (whiteregion) having a specific value; otherwise, it assumes 0.

For each pixel to be processed, a calculation need not be made using allelements of equation (1). The processing can be speeded up by omittingunnecessary calculations as follows.

For example, if nHiddenMark=1, /nHiddenMark=0; if nHiddenMark=0,/nHiddenMark=1. Therefore, if nHiddenMark=1, a value given by:

$\begin{matrix}{{{nHiddenMark} = 1},{a\mspace{14mu}{value}\mspace{14mu}{given}\mspace{14mu}{by}\text{:}\mspace{14mu}\left( {{{nSmallDotOn}\; \times \overset{\_}{nHiddenMark}}\; + {{nLargeDotOn}\; \times {nHiddenMark}}} \right)}} & (2)\end{matrix}$may be used as the value of nLargeDotOn, if nHiddenMark=0, a value givenby equation (2) may be used as the value of nSmallDotOn.

Also, the value of nCamouflage is multiplied by the result of all othervalues in parentheses, and if ncamouflage=0, nWriteDotOn=0. Therefore,if ncamouflage=0, a calculation of equation (2) after ncamouflage can beomitted.

Since an image, which has a height and width equal to least commonmultiples of those of the background threshold pattern 116, latent-imagethreshold pattern 114, copy-forgery-inhibited pattern basic image 115,and camouflage region designation image 117, becomes a minimum unit ofrepetition in the copy-forgery-inhibited pattern image to be generated,the copy-forgery-inhibited pattern image generation unit 101 generatesonly a portion of the copy-forgery-inhibited pattern image as theminimum unit of repetition, and repetitively arranges that portion ofthe copy-forgery-inhibited pattern image in a tile pattern to match thesize of the input background image, thus shortening the processing timerequired to generate the copy-forgery-inhibited pattern image 118.

In step S205, the calculation result (the value of nWriteDoton) in stepS204 is checked. If nWriteDotOn=1 the flow advances to step S206; ifnWriteDotOn=0, the flow advances to step S207.

In step S206, a process for writing a corresponding pixel value in a dotupon printing is executed. The pixel value can be changed depending onthe color of the copy-forgery-inhibited pattern image 118. When a blackcopy-forgery-inhibited pattern is to be generated, the pixel to beprocessed of the input background image 112 is set to be black. Inaddition, if cyan, magenta, or yellow is set in correspondence with thetoner or ink color of the printer, a color copy-forgery-inhibitedpattern image 118 can be generated.

If the input background image 112 is image data which is formed of oneto several bits per pixel, an index color can be used to express a pixelvalue. The index color is an expression method of image data. That is,each color information that frequently appears in a target color imageis set as an index (for example index 0=white, index 1=cyan, and thelike), and each pixel value is expressed by the number of the index thatdescribes the color information (for example, the first pixel value isthe value of index 1, the second pixel value is the value of index 2, .. . ).

It is checked in step S207 if all the pixels of the region to beprocessed of the input background image 112 have been processed. If allthe pixels of the region to be processed of the input background image112 have been not processed yet, the flow advances to step S208 toselect the next pixel to be processed, and the processes in steps S204to S206 are repeated. If all the pixels of the region to be processed ofthe input background image 112 have been processed, the flow advances tostep S209 to end the image process in the copy-forgery-inhibited patternimage generation unit 101. With the above process, thecopy-forgery-inhibited pattern image 118 can be generated by applyingthe image process to the input background image.

A dot layout method in the latent-image part and background-image partin this embodiment will be described below. This embodiment will explaina case wherein the latent-image part is generated based on thedot-concentration dither matrix, and the background-image part isgenerated based on the dot-scattering dither matrix. As a typicaldot-concentration dither matrix used to generate the latent-image part,a spiral dither matrix is prevalent.

FIG. 3 shows an example of a 4×4 spiral dither matrix. Threshold valuesof the 4×4 spiral dither matrix are laid out in a spiral pattern so thattheir numerical values increase in turn from the center.

FIG. 4 shows threshold patterns (dot layouts) obtained by applying athreshold process to predetermined input image signals using the 4×4spiral dither matrix shown in FIG. 3. Referring to FIG. 4, referencenumerals 401, 402, and 403 respectively denote threshold patternsobtained by applying a threshold process to input image signals 3, 6,and 9 using the dither matrix in FIG. 3. In each of the thresholdpatterns (dot layouts) obtained in this case, dots are laid out to beconcentrated.

On the other hand, as a typical dot-scattering dither matrix used toform the background-image part, a Bayer dither matrix is prevalent. ABayer N×N dither matrix is given by:

$D_{N} = \begin{bmatrix}{4D_{N/2}} & {{4D_{N/2}} + {2U_{N/2}}} \\{{4D_{N/2}} + {3U_{N/2}}} & {{4D_{N/2}} + U_{N/2}}\end{bmatrix}$where N is the power of 2, and U_(N) is an N×N matrix, each element ofwhich is 1.

FIG. 5 shows an example of a 4×4 Bayer dither matrix. A thresholdpattern generated by applying dithering to an arbitrary input imagesignal using the Bayer dither matrix is designed to scatter respectivedots.

FIG. 6 shows threshold patterns (dot layouts) obtained by applying athreshold process to predetermined input image signals using the 4×4Bayer dither matrix shown in FIG. 5. Referring to FIG. 6, referencenumerals 601, 602, and 603 respectively denote threshold patternsobtained by applying a threshold process to input image signals 2, 4,and 5 using the dither matrix in FIG. 5. In each of the thresholdpatterns (dot layouts) obtained in this case, dots are laid out to bescattered. In the Bayer dither matrix, respective elements of athreshold matrix are laid out in turn at positions where they do notcontact each other if possible, and threshold patterns have lattice-likedot layouts. In Bayer dithering, periodic texture often stands out dueto a matrix with increasing dither matrix size, but a periodic finepattern is obtained at a specific gray level as a merit.

In this embodiment, a case will be mainly explained wherein the Bayerdither matrix is used as that used for the background. However, thepresent invention is not limited to the Bayer dither matrix. Otherdot-scattering dither matrices may be used.

For example, a blue noise mask is an example of dot-scattering dithermatrices used for background. With this blue noise mask, all thresholdpatterns at an arbitrary gray level have blue noise characteristics, andthe distribution of black pixels which form each threshold pattern israndom but has high uniformity, thus obscuring granularity. The bluenoise characteristics mean that an output pattern of dots upon settingan arbitrary gray level is locally a periodic and isotropic, and has asmall number of low-frequency components. A threshold pattern generatedusing the blue noise mask can obtain a visually preferable outputpattern: generation of moire is prevented, paper feed nonuniformity isobscured, and so forth.

In place of the blue noise mask, a dot-scattering dither matrix that canform a threshold pattern at a specific or arbitrary gray level, which isperiodic (or pseudo-periodic) and anisotropic and has a small number oflow-frequency components may be used. In this embodiment, thebackground-image part may be formed using error diffusion although it isnot a method using a threshold pattern. When a background thresholdpattern is generated using the aforementioned Bayer dither matrix orblue noise mask, the value of nSmallDotOn in equation (1) can be readout with reference to the background threshold pattern. On the otherhand, when error diffusion is used, the sum of a gray levelcorresponding to a background density and errors distributed fromsurrounding pixels is compared with a predetermined threshold value foreach pixel to determine ON/OFF of dots in a pixel to be processed, andthe value determined in this case may be used as that of nSmallDotOn. Atthis time, errors generated upon ON/OFF of dots are distributed toneighboring pixels after they are weighted. The pixel value of a pixelto be processed is the sum of an original input pixel valuecorresponding to the background density and the distributed error.

Assume that gray levels corresponding to background densities areprepared in advance as in the background threshold pattern. Errordiffusion requires a long processing time as its demerit, but can obtainan image with good visual characteristics in which dots are uniformlyscattered as its merit. Since error diffusion is already well known, adetailed description thereof will be omitted in this embodiment.Likewise, a method obtained by improving error diffusion can be applied.

Also, threshold patterns corresponding to respective gray levels neednot be generated based on a dither matrix. A background thresholdpattern and latent-image threshold pattern may be independentlygenerated for each gray level. In this case, threshold patterns withhigh image quality can be corrected for respective gray levels, as amerit.

FIG. 7 is a view for comparing the area ratios of the backgroundthreshold pattern and latent-image threshold pattern. As shown in FIG.7, let X_S and Y_S be the height and width of the background dithermatrix, T_S be the gray level of an input image signal, X_L and Y_L bethe height and width of the latent-image dither matrix, and T_L be thegray level of an input image signal.

Then, the occupation ratio of black pixels in the background thresholdpattern is given by P_S=T_S/(X_S*Y_S), and that of black pixels in thelatent-image threshold pattern is given by P_L=T_L/(X_L*Y_L).

FIG. 8 show graphs showing the relationships between the area ratios ofblack pixels of threshold patterns obtained by applying a thresholdprocess to input image signals using a dither matrix, and the densitiesupon printing the threshold patterns. In dithering, since the area ratioof black pixels changes depending on the gray levels of input imagesignals, the abscissa of FIG. 8 may be considered as the gray levels ofinput image signals.

Note that the dither matrix of the background-image part (backgroundthreshold pattern) and the dither matrix of the latent-image part(latent-image threshold pattern) need not always have the same sidesize, but they may have different sizes. For example, when thebackground dither matrix and latent-image dither matrix have identicalgrayscale characteristics (e.g., 801), if the values on the abscissa(the area ratios of black pixels) are nearly equal to each otherirrespective of the sizes of the dither matrices of the background-imagepart and latent-image part, i.e., if the gray levels T_S and T_L ofinput image signals that make P_S and P_L nearly equal to each other areused, the background threshold pattern and latent-image thresholdpattern have nearly equal densities, and a copy-forgery-inhibitedpattern image that can obscure a latent-image can be generated.

However, in practice, the background and latent-image dither matrices donot always have identical grayscale characteristics depending on thecharacteristics of a printer.

For example, assume that the grayscale characteristics of thelatent-image dither matrix are expressed by a moderate S curve (e.g.,802), and those of the background dither matrix are expressed by a steepS curve (e.g., 803). In such case, even when the area ratios of blackpixels of the background and latent-image threshold patterns are set tobe nearly equal to each other, the densities of the background-image andlatent-image parts do not become equal to each other upon printing.

By appropriately adjusting one of the background-image and latent-imageparts or input image signals to both the dither matrices, the density ofone of the background-image and latent-image parts can be approximate tothat of the other upon printing.

If the number of gray levels that can be expressed by the background orlatent-image dither matrix is large, the density of the background orlatent-image part can be finely adjusted by adjusting the gray level ofan input image signal.

When the latent-image dither matrix is the dot-concentration dithermatrix, as shown in FIG. 3, and when the gray level of an input imagesignal becomes equal to or lower than a given value, isolated dots areformed, and the latent-image part is prone to disappear. On the otherhand, when the gray level of an input image signal becomes equal to orhigher than a given value, dots are concentrated, and groups of dotsthemselves that form the latent-image are clearly visually recognized.

Therefore, in the latent-image dither matrix, the gray levels ofpossible input image signals preferably fall within a predeterminedrange. In the latent-image dither matrix shown in FIG. 3, even when thedither matrix size changes, if the gray level of an input image signalremains the same, nearly identical concentrated dot layouts can beobtained. Therefore, by maintaining constant the gray level of an inputimage signal to the latent-image dither matrix, and changing the dithermatrix size, the density per unit area can be changed.

On the other hand, when the background dither matrix is thedot-scattering dither matrix, shown in FIG. 8, the density can bechanged by changing the gray level of an input image signal whileuniformly printing dots on the entire image. Therefore, the backgrounddither matrix having a broader grayscale range (i.e., a larger dithermatrix size) excels in density adjustment of the background-image part.

When a copy-forgery-inhibited pattern is to be output using a printer,an adjustment function of adjusting the density variations of theprinter is required. Such function will be described in detail later.

FIG. 9 is a view showing the generation process of acopy-forgery-inhibited pattern image using the copy-forgery-inhibitedpattern compositing/printing apparatus shown in FIG. 1. Referring toFIG. 9, reference numerals 901, 902, and 903 respectively denote alatent-image threshold pattern, background threshold pattern, andcopy-forgery-inhibited pattern basic image; and 904, acopy-forgery-inhibited pattern image generated based on equation (1).Note that no camouflage pattern is introduced in the generation stage ofthe image 904.

In the copy-forgery-inhibited pattern image 904 shown in FIG. 9, a groupof dots as a combination of the latent-image and background thresholdpatterns is generated at a boundary portion of the latent-image andbackground in the copy-forgery-inhibited pattern basic image 903, asindicated by a circled region 910. Such group of dots is readilygenerated when the boundary between the latent-image and background ofthe copy-forgery-inhibited pattern basic image 903 is not synchronizedwith the size of the latent-image threshold pattern. Also, since suchgroups of dots concentratedly appear at the boundary between thelatent-image and background of the copy-forgery-inhibited pattern basicimage, an approximate shape of the latent-image stands out, thusreducing the effect of the copy-forgery-inhibited pattern as a demerit.

Therefore, in order to generate a copy-forgery-inhibited pattern imagewith high image quality, a process that prevents groups of dots frombeing generated at the boundary between the latent-image and backgroundin the copy-forgery-inhibited pattern basic image is required.

In this embodiment, the process that prevents groups of dots from beinggenerated at the boundary between the latent-image and background in thecopy-forgery-inhibited pattern basic image will be referred to as a“boundary process” hereinafter. As an example of this boundary process,a method of reading only the pixel values of the repetitively laid-outcopy-forgery-inhibited pattern basic images, which correspond to thecenters of repetitively laid out latent-image threshold patterns (apixel which is moved from the upper left position by those which areobtained by omitting the half of one side of each latent-image thresholdpattern is used as the center) to set values of HiddenMarkLattice, andprocessing pixels which belong to one latent-image threshold patternusing identical values of HiddenMarkLattice is available. Thisprocessing method is described by:nWriteDotOn=nCamouflage×(nSmallDotOn×nHiddenMarkLattice+nLargeDotOn×nHiddenMarkLattice)

Using this method, each latent-image threshold pattern is formedtogether with a white background unless it is located at the end of animage. Therefore, when the white background is present around blackpixels of the latent-image threshold pattern, it serves as a buffer zoneto prevent black pixels of the latent-image and background thresholdpatterns from contacting, and the boundary between the latent-image andbackground designated by the copy-forgery-inhibited pattern basic imagecan be prevented from standing out.

In FIG. 9, reference numeral 905 denotes a copy-forgery-inhibitedpattern image that has undergone the boundary process. As can be seenfrom the image 905, no groups of dots as combinations of thelatent-image and background threshold patterns are generated at theboundary between the latent-image and background designated by thecopy-forgery-inhibited pattern basic image.

As an example of another boundary process, a method of pre-processingthe boundary between the latent-image and background in the inputcopy-forgery-inhibited pattern basic image in synchronism with the sizeof each latent-image threshold pattern is available. With this method,latent-image threshold patterns are repetitively laid out in thecopy-forgery-inhibited pattern basic image, and the pixel values of thecopy-forgery-inhibited pattern basic image, corresponding to the centersof the latent-image threshold patterns, are read, thus generating asub-sampled copy-forgery-inhibited pattern basic image. The sub-sampledcopy-forgery-inhibited pattern basic image is enlarged, so that the sizeof one pixel becomes an integer multiple of that of the latent-imagethreshold pattern, thereby preparing a modified copy-forgery-inhibitedpattern basic image. Finally, a copy-forgery-inhibited pattern image isgenerated based on equation (1) with respect to the modifiedcopy-forgery-inhibited pattern basic image, thus generating acopy-forgery-inhibited pattern image free from any groups of dotsindicated by 910.

When the aforementioned “boundary process” is added to thecopy-forgery-inhibited pattern image generation unit 101, thecopy-forgery-inhibited pattern basic image need not be prepared bysynchronizing the boundary between the latent-image and backgrounddesignated by the copy-forgery-inhibited pattern basic image with thesize of each latent-image threshold pattern, resulting high usabilityfor the user.

FIG. 12A partially shows a copy-forgery-inhibited pattern imagegenerated by the copy-forgery-inhibited pattern image generation unit101 by the boundary process. Upon generating the copy-forgery-inhibitedpattern image shown in FIG. 12A, the images 1001 and 1002 shown in FIG.10 are respectively used as the copy-forgery-inhibited pattern basicimage and camouflage region designation image, and the images 1101 and1102 shown in FIG. 11 are respectively used as the latent-imagethreshold pattern and background threshold pattern. Note that the brokenlines which bound the images 1001, 1002, 1101, and 1102 indicate theimage boundaries, which are not present in an actual image. Since thecopy-forgery-inhibited pattern image shown in FIG. 12A has undergone theboundary process, the boundary between the latent-image and backgrounddoes not suffer any dot grouping phenomenon, and the latent-image partbecomes harder to recognize.

[Large/Small Dot Checkered Pattern Layout]

In the following description, the method of repetitively laying out theaforementioned latent-image threshold patterns in a tile pattern will bereferred to as a “tile layout of latent-image threshold patterns in thelatent-image part” or simply as a “tile layout”.

Note that a “checkered pattern” in the present invention indicates apattern in which regions having predetermined shapes alternately andrepetitively appear, and is an expression including a lattice patternand the like. That is, layouts and shapes are not particularly limitedas long as different images are laid out in a tile pattern atpredetermined intervals.

The layout method of latent-image threshold patterns will be describedin detail below.

In general, it is known that the two-dimensional spatial frequencycharacteristics of human vision have dependence in the spatialdirection, and the visual resolution drops with respect to a pattern inwhich dots are laid out at an angle of 45°. Also, in halftone dotprinting, it is a common practice to lay out K (black) dots which arenormally most conspicuous at an angle of 45° (a screen angle of 45°).

Therefore, in the copy-forgery-inhibited pattern image as well,latent-image threshold patterns (large dots) of the latent-image partare laid out to be approximate to a halftone dot screen at a screenangle of 45°, thus more obscuring the latent-image part.

In this embodiment, by laying out latent-image threshold patterns (largedots) in a checkered pattern, a layout approximate to a halftone dotscreen at a screen angle of 45° can be realized.

Initially, a flag nChecker used to divide the latent-image part into tworegions (a region where large dots are written and a region where nolarge dots are written) is prepared. Note that the flag nChecker is setat a predetermined value (0 or 1) at the upper left position of an imageor the embedding start position of a copy-forgery-inhibited patternimage. Next, every time the dot write region shifts to aright-neighboring or lower-neighboring latent-image threshold pattern,the value of the flag nchecker is inverted from the previous value. Thatis, if the previous value is 0, it is inverted to 1; and vice versa.

When the value of the flag nChecker is changed in this way, a checkeredpattern in which 0 and 1 are switched for respective repetition units ofthe latent-image threshold patterns can be generated.

The latent-image threshold patterns (large dots) are written only whenthe copy-forgery-inhibited pattern basic image indicates thelatent-image part (nHiddenMarkLattice=1) and the flag nChecker thatdefines the checkered pattern is 1. This process can be described as alogical operation by:

${nWriteDotOn} = {{nCamouflage}\; \times \left( {{{nSmallDotOn}\; \times \overset{\_}{nHiddenMarkLattice}}\; + {{nLargeDotOn}\; \times \left( {{nHiddenMarkLattice}\; \times {nChecker}} \right)}} \right)}$

FIG. 12B shows an example of a copy-forgery-inhibited pattern image withthe checkered pattern layout, which is generated by controlling ON/OFFof dots on the basis of the aforementioned logical expression. In FIG.12B, latent-image threshold patterns are laid out in the checkeredpattern, and the spatial frequency produced by the periodicity of groupsof dots of the latent-image threshold patterns (large dots) and spacesbecomes relatively inconspicuous.

In this embodiment, the method of laying out latent-image thresholdpatterns in the latent-image part in a checkered pattern will bereferred to as a “checkered pattern layout of latent-image thresholdpatterns in the latent-image part” or simply as “checkered patternlayout”.

In this “checkered pattern layout”, since latent-image thresholdpatterns may or may not be laid out in some cases at the boundarybetween the latent-image part and background-image part of thecopy-forgery-inhibited pattern basic image, the dot density at theboundary between the latent-image part and background-image part becomesnonuniform, and a boundary line often becomes conspicuous. In such case,the latent-image part and background-image part can be switched forrespective pixels of the copy-forgery-inhibited pattern basic image inplace of latent-image threshold patterns.

This process can be described by:

${nWriteDotOn} = {{nCamouflage} \times \left( {{{nSmallDotOn} \times \overset{\_}{nHiddenMark}} + {{nLargeDotOn} \times \left( {{nHiddenMark} \times {nChecker}} \right)}} \right)}$

In the aforementioned “checkered pattern layout”, groups of dots oflatent-image threshold patterns are laid out to be approximate to ahalftone dot screen at a screen angle of 45°, the visual characteristicscan be improved, but a white background region of latent-image thresholdpatterns becomes conspicuous due to contrast from the background of thecopy-forgery-inhibited pattern image and groups of dots of latent-imagethreshold patterns with increasing density of the copy-forgery-inhibitedpattern image.

In order to obscure the white background region of each latent-imagethreshold patterns, a case will be examined below wherein thelatent-image part is divided into two regions, latent-image thresholdpatterns are laid out in one region, and background threshold patternsare laid out in the other region.

More specifically, the flag nChecker is switched between 1 and 0 forrespective latent-image threshold patterns like the checkered pattern,latent-image threshold patterns are laid out in a region whichcorresponds to the latent-image part and in which the flag nChecker isone bit (e.g., 1) (this region will be referred to as region Ahereinafter), and background threshold patterns are laid out in a regionwhich corresponds to the latent-image part and in which the flagnChecker is the other bit (e.g., 0) (this region will be referred to asregion B hereinafter).

ON/OFF of dots of the copy-forgery-inhibited pattern image can bedescribed by:

${nWriteDotOn} = {{nCamouflage}\; \times \left( {{{nSmallDotOn}\; \times \left( \overset{\_}{{nHiddenMarkLattice}\; \times {nChecker}} \right)} + {{nLargeDotOn}\; \times \left( {{nHiddenMarkLattice}\; \times {nChecker}} \right)}} \right)}$If nCamouflage=1,

-   when nHiddenMarkLattice=0 and nChecker=0,-   nWriteDotOn=nSmallDotOn-   when nHiddenMarkLattice=0 and nChecker=1,-   nWriteDotOn=nSmallDotOn-   when nHiddenMarkLattice=1 and nChecker=0,-   nWriteDotOn=nSmallDotOn-   when nHiddenMarkLattice=1 and nChecker=1,-   nWriteDotOn=nLargeDotOn    In this way, latent-image threshold patterns are laid out in only    region A of the latent-image part.

In the following description, the method of dividing the latent-imagepart into two regions, and laying out both the latent-image andbackground threshold patterns will be referred to as a “crossover layoutof latent-image and background threshold patterns in the latent-imagepart” or simply as a “crossover layout”. The method of dividing thelatent-image part into a checkered pattern for respective latent-imagethreshold patterns can be referred to as a checkered pattern typecrossover layout.

FIG. 12C shows an example of a copy-forgery-inhibited pattern image withthe checkered pattern type crossover layout, which is generated usingthe above equation. FIG. 12D is an enlarged view of a region designatedby the copy-forgery-inhibited pattern basic image in FIG. 12C.

In FIG. 12C, since latent-image threshold patterns have substantiallythe same layout as that of a halftone dot screen at a screen angle of45°, the spatial frequency due to the periodicity of latent-imagethreshold patterns (large dots) become inconspicuous. This is a merit ofthe “checkered pattern layout” in terms of image quality.

Also, the density per unit area becomes uniform at the boundary linebetween the latent-image part and background-image part, and an effectof obscuring the boundary line can be obtained. This is a merit of thetile layout in terms of image quality. Also, since the aforementioned“crossover layout” obscures the latent-image part, it is a merit of the“tile layout” in terms of image quality.

Furthermore, in the aforementioned “crossover layout”, paper white(plain) regions formed due to the presence of groups of dots oflatent-image threshold patterns have substantially the same layout as athat of a halftone dot screen at a screen angle of 45°. Although paperwhite regions become more conspicuous with increasing density of thecopy-forgery-inhibited pattern image, the aforementioned “crossoverlayout” can also visually obscure paper white regions, and not onlygroups of dots but also paper white regions become visuallyinconspicuous.

Note that latent-image threshold patterns of the latent-image part inthe aforementioned “crossover layout” are about the half of those in thetile layout, and the density of the latent-image that emerges uponcopying is lower than that of the “tile layout”.

However, such low density does not pose any serious problem when thelatent-image part has a density that can be easily recognized by aperson. The on-demand copy-forgery-inhibited pattern generation methodby a printer is susceptible to the density variations of the printer.The presence of not only density variations due to an environment oraging but also those in the plane of paper can provide an effect ofmaking it harder to recognize the latent-image of thecopy-forgery-inhibited pattern image.

Therefore, the aforementioned “crossover layout” can achieve not only aneffect of obscuring the latent-image of the copy-forgery-inhibitedpattern image but also an effect of allowing the on-demandcopy-forgery-inhibited pattern generation method by a printer whichreadily causes density variations to stably generate acopy-forgery-inhibited pattern image in which a latent-image isinconspicuous. As a result, the frequency of test printing processes tobe described in detail later) can be reduced.

When the aforementioned “crossover layout” is used, the density of thelatent-image part (a region of nHiddenMarkLattice=1) is given by thedensity of background threshold patterns/2+the density of latent-imagethreshold patterns/2. Therefore, even when copy-forgery-inhibitedpattern density parameters used to generate a copy-forgery-inhibitedpattern image in which the print densities of the latent-image part andbackground-image part are approximate to each other in the “tile layout”are directly applied to the “crossover layout”, the print densities ofthe latent-image part and background-image part can be substantiallysimilarly approximate to each other as a merit.

That is, the “tile layout” and “crossover layout” generate substantiallythe same density on the entire copy-forgery-inhibited pattern image, anduse substantially the same copy-forgery-inhibited pattern densityparameters which are used to generate a copy-forgery-inhibited patternimage in which the print densities of the latent-image part andbackground-image part are approximate to each other. Therefore, the“tile layout” and “crossover layout” can use commoncopy-forgery-inhibited pattern density parameters.

By exploiting a feature of substantially approximatecopy-forgery-inhibited pattern density parameters, means that allows theuser who wants to generate a copy-forgery-inhibited pattern image toselect one of two options from an input menu can be provided.

-   -   Normal mode (tile layout)    -   High image quality mode (crossover layout)

As a variation of the aforementioned “crossover layout”, a thirdthreshold pattern which is different from a background threshold patternmay be used, and latent-image threshold patterns and third thresholdpatterns may be laid out to cross in a checkered pattern.

In this case, ON/OFF of dots of a copy-forgery-inhibited pattern imagecan be described by:

${nWriteDotOn} = {{nCamouflage}\; \times \left( {{{nSmallDotOn}\; \times \overset{\_}{nHiddenMarkLattice}}\; + {{nThirdDotOn}\; \times \left( {{nHiddenMarkLattice}\; \times \overset{\_}{nChecker}} \right)} + {{nLargeDotOn}\; \times \left( {{nHiddenMarkLattice}\; \times {nChecker}} \right)}} \right)}$where nThirdDotOn is the third threshold pattern.

-   If ncamouflage=1,-   when nHiddenMarkLattice=0 and nChecker=0,-   nWriteDotOn=nSmallDotOn-   when nHiddenMarkLattice=0 and nChecker=1,-   nWriteDotOn=nSmallDotOn-   when nHiddenMarkLattice=1 and nChecker=0,-   nWriteDotOn=nThirdDotOn-   when nHiddenMarkLattice=1 and nChecker=1,-   nWriteDotOn=nLargeDotOn

In this way, various threshold patterns having different features asthat of the latent-image threshold pattern can be selected as the thirdthreshold pattern. When the user wants to clear the third thresholdpattern after copying, the third threshold pattern may be generatedusing the dot-scattering dither matrix.

The third threshold pattern including a plurality of dot groupsrelatively smaller than those of the latent-image threshold pattern maybe generated.

The third threshold pattern may be generated using a dot-concentrationdither matrix which has a feature different from that for thelatent-image threshold pattern.

A binary pattern having the same size as the latent-image thresholdpattern may be manually generated for each gray level.

In this embodiment when the latent-image part designated by thecopy-forgery-inhibited pattern basic image is divided into a region madeup of the latent-image threshold patterns (region A) and a region madeup of the third threshold patterns (region B), information like acheckered pattern which is switched for respective units as large as thelatent-image threshold pattern is generated. However, the latent-imagepart may be divided using other kinds of information.

For example, information such as random noise which is randomly switchedbetween 0 and 1 for respective latent-image threshold patterns, or abinary image having blue noise characteristics with few low-frequencycomponents and many high-frequency components may be used, thus adoptingvisually preferred various binary images. Note that the value of theflag nchecker is switched between 0 and 1 for respective latent-imagethreshold patterns in the same manner as in the checkered pattern.

According to this embodiment, a binary image with a checkered pattern isapplied in addition to the copy-forgery-inhibited pattern basic imagethat designates the latent-image part and background-image part, groupsof dots are laid out in a region which is designated as the latent-imagepart and corresponds to one region (region A) of the checkered pattern.At the same time, dots having features different from those laid out inregion A are laid out in a region which is also designated as thelatent-image part and corresponds to the other region (region B) of thecheckered pattern. With this arrangement, the layout of groups of dotsis set to be equivalent to that at a screen angle of 45° in a halftonedot screen to realize an effect of making it harder to perceive forhuman. Furthermore, since dots are laid out in each region B, even apaper-white region which is always formed around groups of dots andbecomes conspicuous due to the density difference from thecopy-forgery-inhibited pattern image has a layout equivalent to that ata screen angle of 45° in halftoning, and can be visually obscured.

In the aforementioned embodiment, the area ratio of regions A and B isset to be 1:1 upon switching regions A and B in the checkered pattern.However, the present invention is not limited to such specific arearatio.

For example, if regions A and B are switched on the basis of the valuesof white and black pixels of a binary pattern (which has blue noisecharacteristics) obtained by binarizing a blue noise mask by apredetermined gray level, the area ratio of regions A and B changesdepending on the gray level used to binarize the blue noise mask.

That is the number of large dots that remain after copying increaseswith increasing area of region A, thus providing a merit of making iteasier to recognize an image to be visualized after copying. Therefore,the area ratio of regions A and B can be arbitrarily determinedaccording to the purpose intended.

In this embodiment, the latent-image part is divided into two regions,i.e., regions A and B. However, the present invention is not limited totwo regions, but the latent-image part may be divided into three or moreregions. For example, the latent-image part may be divided into threeregions, which are specified as a large dot region, small dot region,and no-dot generation region (plain region), and acopy-forgery-inhibited pattern image may be generated to arbitrarily layout these regions, thus also achieving the object of the presentinvention.

The process in the composition unit 102 that composites thecopy-forgery-inhibited pattern image generated by the aforementionedcopy-forgery-inhibited pattern image generation unit 101 and an inputdocument image (e.g., a slip, certificate, or the like) will bedescribed below.

FIG. 13 shows a composition process of an input document image andcopy-forgery-inhibited pattern image. Referring to FIG. 13, referencenumeral 1301 denotes text attribute data; 1302, graphic attribute data;and 1303, an image attribute copy-forgery-inhibited pattern image.

The composition unit 102 superposes the images 1301 to 1303 inaccordance with the priority order (layer structure) associated with alayout in software manner using a rendering interface of an OS, thusgenerating an image 1304 obtained by compositing the text attributedata, graphic attribute data, and image attribute copy-forgery-inhibitedpattern image. This process is substantially the same as screenrendering (display rendering) in drawing software as a generalapplication of a computer. Note that the composition unit 102 mayexecute a unique image composition process independent from therendering interface process of the OS.

In the example shown in FIG. 13, the image attributecopy-forgery-inhibited pattern image 1303 is superposed as the lowermostlayer of the text attribute data 1301 and graphic attribute data 1302.For example, at a position where the image attributecopy-forgery-inhibited pattern image 1303 and text attribute data 1301are to be superposed, the text attribute data 1301 is preferentiallyrendered. Therefore, the copy-forgery-inhibited pattern image isappropriately laid out on the background of the input document image,and does: not lower the visibility of the text attribute data andgraphic attribute data.

In the example shown in FIG. 13, the copy-forgery-inhibited patternimage 1303 has the same size as that of the input image. When thecopy-forgery-inhibited pattern image is to be superposed only on a localregion, the copy-forgery-inhibited pattern image generation unit 101inputs an input background image with a size corresponding to the localregion, and generates only a copy-forgery-inhibited pattern image thatmatches the input image size, and the composition unit 102 can compositeit to the input document image. As the copy-forgery-inhibited patternimage to be generated has a smaller size, the processing in thecopy-forgery-inhibited pattern image generation unit 101 can be speededup.

The copy-forgery-inhibited pattern composited output document imageoutput from the composition unit 102 may be data expressed by therendering interface of the OS or a bitmap image as a composition result.The copy-forgery-inhibited pattern composited output document image issent to the next print data processing unit 103.

The print data processing unit 103 receives the copy-forgery-inhibitedpattern composited output document image composited by the compositionunit 102 as rendering information via the rendering interface of the OS,and sequentially converts it into commands. At this time, the unit 103executes image processes such as a color matching process, RGB-CMYKconversion, halftone process, and the like. The print data processingunit 103 sends a data format (e.g., a data format described in the pagedescription language or a data format rasterized to a print bitmap) thatcan be interpreted by the print unit 104 as copy-forgery-inhibitedpattern composited output document image data to the next print unit104.

The print unit 104 prints out a copy-forgery-inhibited patterncomposited output document in accordance with the information of theinput copy-forgery-inhibited pattern composited output document imagedata.

FIG. 14 shows a method of compositing a copy-forgery-inhibited patternimage to an input document image which has already been composited withvarious images and has no layer structure. Referring to FIG. 14,reference numeral 1401 denotes an input document image which has alreadybeen composited with various images and has no layer structure; and1402, a region which has a specific pixel value (e.g., a whitebackground region) and at which a copy-forgery-inhibited pattern imageis to be laid out.

Note that the remaining region of the input document image 1401 has nospecific value (e.g., it is not a white background region).

FIG. 15 is a block diagram showing the internal arrangement of acopy-forgery-inhibited pattern compositing/printing apparatus forcompositing a copy-forgery-inhibited pattern image to an input documentimage which has already been composited with various images and has nolayer structure. The copy-forgery-inhibited pattern compositing/printingapparatus shown in FIG. 15 is suited to a case wherein acopy-forgery-inhibited pattern image is to be composited to an image(e.g., 1401) which has already been composited with various images andhas no layer structure.

As shown in FIG. 15, this copy-forgery-inhibited patterncompositing/printing apparatus comprises a copy-forgery-inhibitedpattern image composited output document generation unit 1501, printdata processing unit 1502, and print unit 1503. Thecopy-forgery-inhibited pattern image composited output documentgeneration unit 1501 receives an input document image, colorinformation, processing region information, latent-image thresholdpattern, background threshold pattern, copy-forgery-inhibited patternbasic image, and camouflage region designation image, and generates andoutputs a copy-forgery-inhibited pattern composited input document.

The copy-forgery-inhibited pattern image composited output documentgeneration unit 1501 detects a region having a specific pixel value(e.g., a white background region) from an input document image,composites a copy-forgery-inhibited pattern image to only that region,and outputs a copy-forgery-inhibited pattern image composited outputdocument image. More specifically, whether or not a pixel valuecorresponding to a copy-forgery-inhibited pattern image is to be writtenin a pixel in the input document image is determined using:

$\begin{matrix}{{nWriteDotOn} = {{nBackground}\; \times {nCamouflage} \times \left( {{{nSmallDotOn}\; \times \overset{\_}{nHiddenMark}}\; + {{nLargeDotOn}\; \times {nHiddenMark}}} \right)}} & (3)\end{matrix}$which is prepared by multiplying equation (3) by an item (nBackground)that refers to the input document image.

Note that nBackground=1 when the input document image is a region (whitebackground region) with a specific pixel value; otherwise,nBackground=0.

As in the copy-forgery-inhibited pattern image generation unit 101 shownin FIG. 1, the copy-forgery-inhibited pattern image composited outputdocument generation unit 1501 can speed up processes by omittingunnecessary calculations. Since nBackground is a multiplication to thewhole equation, equation (3) is calculated for only a pixel withnBackground=1 to determine whether or not a pixel value corresponding toa copy-forgery-inhibited pattern image is written is determined.

Since the copy-forgery-inhibited pattern image composited outputdocument generation unit 1501 executes substantially the same process asthat of the copy-forgery-inhibited pattern image generation unit 101shown in FIG. 1 except that it refers to pixel values of the inputdocument image, a detailed description thereof will be omitted.

The copy-forgery-inhibited pattern image composited output documentimage generated by the copy-forgery-inhibited pattern image compositedoutput document generation unit 1501 is output to the print dataprocessing unit 1502. The print data processing unit 1502 executessubstantially the same process as that in the print data processing unit103 shown in FIG. 1. At this time, the region composited with thecopy-forgery-inhibited pattern image preferably undergoes imageprocesses that skip a color conversion process such as color matching orthe like, so as to prevent a pixel value of one pixel from forming a dotof a mixed color expressed by a plurality of different inks or tonersupon printing.

The print data processing unit 1502 converts the processed data into adata format (e.g., a data format described in the page descriptionlanguage or a data format rasterized to a print bitmap) that can beinterpreted by the print unit 104 and sends it as copy-forgery-inhibitedpattern composited output document image data to the next print unit1503.

The print unit 1503 prints out a copy-forgery-inhibited patterncomposited output document in accordance with the information of theinput copy-forgery-inhibited pattern composited output document imagedata. In this manner, a copy-forgery-inhibited pattern image can becomposited to a region having a specific pixel value (e.g., a whitebackground region) of an input document image, and a composite image canbe output.

According to the aforementioned embodiment, a copy-forgery-inhibitedpattern image can be efficiently laid out and composited to apredetermined region of an input image by executing logical operationsusing background and latent-image threshold patterns as alreadybinarized patterns, a copy-forgery-inhibited pattern basic image as abinary image that designates the latent-image part and background-imagepart, a camouflage region designation image as a binary image thatdesignates a camouflage region, and bit information indicating whetheror not a pixel value of an input image is a predetermined pixel.

Also, a copy-forgery-inhibited pattern image can be generated at highspeed using a small memory size by executing logical operations usingbackground and latent-image threshold patterns as binary images, acopy-forgery-inhibited pattern basic image as a binary image thatdesignates the latent-image part and background-image part, and acamouflage region designation image as a binary image that designates acamouflage region.

Furthermore, a copy-forgery-inhibited pattern image can be efficientlylaid out in a predetermined region (e.g., a white background region) ofan input image by checking if the copy-forgery-inhibited pattern imageis to be composited to the input image by logical operations using bitinformation indicating whether or not the pixel value of an input imageis a predetermined pixel with reference to the pixel value of the inputimage as needed.

The generation method of a copy-forgery-inhibited pattern image and thecomposition method of the copy-forgery-inhibited pattern image and inputdocument image have been explained in detail. However, when acopy-forgery-inhibited pattern image is to be actually output using aprinter, the latent-image part and background-image part are not alwaysoutput at densities the user intended due to various causes.

The causes include density instability depending on various conditionssuch as different engine characteristics of printers, different dithermatrices used to output threshold patterns, individual differences ofprinters, print environments such as humidity, temperature, and thelike, aging of an engine, different paper sheets (media), different inksor toners of printers, and the like. That is, input gray levels optimalto the dither matrices for the background-image part and latent-imagepart are more likely to vary depending on printer models, dithermatrices, printers themselves, print environments, paper sheets, inksand toners, and the like.

Therefore, even when the engine characteristics of printers or printenvironments are different, a copy-forgery-inhibited pattern image mustbe generated after background and latent-image threshold patterns whichhave nearly equal densities upon printing are obtained. However, it ispractically difficult to automatically calculate optimal background andlatent-image threshold patterns in consideration of all variationfactors including variations due to a print environment.

Hence, a function of obtaining background and latent-image thresholdpatterns which can set the background-image and latent-image parts tohave substantially the same densities for each printer before executionof the copy-forgery-inhibited pattern compositing/printing apparatusi.e. a copy-forgery-inhibited pattern density calibration function needbe implemented.

As a method of implementing the copy-forgery-inhibited pattern densitycalibration function, a method of changing the gray level of an inputimage signal input to one or both of the background dither matrix andlatent-image dither matrix so as to adjust the densities to besubstantially equal to each other may be used.

FIG. 16 shows a latent-image threshold pattern and background thresholdpatterns obtained by applying a threshold process to the gray levels ofa plurality of input image signals using a dither matrix. Referring toFIG. 16, reference numeral 1601 denotes a latent-image threshold patternobtained by inputting a gray level “6” to a latent-image dither matrixwhich is defined by 10 pixels per side. The area ratio of black pixelsis 6%.

On the other hand, reference numerals 1602 to 1604 denote backgroundthreshold patterns obtained by respectively inputting gray levels “12”,“16”, and “20” to a background dither matrix which is defined by 16pixels per side. The area ratios of black pixels of these patterns arerespectively 4.69%, 6.25%, and 7.81%. If a background dither matrix isdefined by 4×4 pixels, and undergoes density adjustment by changing thegray level of an input image signal, the area ratio of black pixels hasonly a range of 17 steps (=4×4+1), and only a change in gray level ofabout 6% per step is given. For this reason, a delicate densityadjustment cannot be done.

However, the density of each of the background threshold patterns 1602to 1604, which are output from the dither matrix which can express manygray levels, can be finely adjusted by selecting the gray level of aninput image signal, and such patterns are suitable for densitycalibration.

An overview of a copy-forgery-inhibited pattern test printing processrequired to implement the copy-forgery-inhibited pattern densitycalibration function will be explained below. The copy-forgery-inhibitedpattern test printing process can be implemented by an application orprinter driver on a computer.

FIG. 22 is a block diagram showing the internal arrangement of anapparatus that executes a copy-forgery-inhibited pattern test printingprocess. As shown in FIG. 22, the apparatus that executes thecopy-forgery-inhibited pattern test printing process has a settinginformation input unit 2201, pattern generation unit 2202, test printcopy-forgery-inhibited pattern image generation unit 2203, print dataprocessing unit 2204, and print unit 2205.

Note that the apparatus arrangement is not limited to this, and needonly have an arrangement that can solve the problems of the presentinvention. Also, the apparatus need not be exclusively used for thecopy-forgery-inhibited pattern test printing process.

The setting information input unit 2201 executes a process for readingsetting information from an initial setting file that saves settinginformation, or a process for receiving setting information input via auser interface. The pattern generation unit 2202 generates patternsrequired to generate a copy-forgery-inhibited pattern on the basis ofthe setting information input from the setting information input unit2201, and outputs them to the next test print copy-forgery-inhibitedpattern image generation unit. In case of this embodiment, the patternsto be generated based on the input setting information includes abackground threshold pattern and latent-image threshold pattern. In thecopy-forgery-inhibited pattern test printing process, the patterngeneration unit 2202 generates a plurality of background thresholdpatterns and latent-image threshold patterns.

The test print copy-forgery-inhibited pattern image generation unit 2203generates a test block copy-forgery-inhibited pattern image on the basisof the patterns input from the pattern generation unit 2202. Details ofthe test print copy-forgery-inhibited pattern image generation unit 2203will be described later.

The print data processing unit 2204 applies required image processes tothe test print copy-forgery-inhibited pattern image generated by thetest print copy-forgery-inhibited pattern image generation unit 2203.Note that the print data processing unit applies image processes to thetest print copy-forgery-inhibited pattern image so as to prevent thepixel value (cyan, magenta, yellow, or black) of acopy-forgery-inhibited pattern image from being expressed by any mixedcolor formed by mixing a plurality of inks or toners upon printing. Thetest print copy-forgery-inhibited pattern image that has undergone therequired image processes is converted into a data format (e.g., a dataformat described in the page description language or a data formatrasterized to a print bitmap) that can be interpreted by the print, andis sent to the next print unit 2204. The print unit 2204 prints out atest print copy-forgery-inhibited pattern image in accordance with theinput data.

A test print sheet, on which a plurality of copy-forgery-inhibitedpattern images that are generated by the test printcopy-forgery-inhibited pattern image generation unit 2203 and are formedby changing the densities of both the background-image and latent-imageparts are two-dimensionally laid out, will be explained below.Respective copy-forgery-inhibited pattern image laid out on the sheetwill be referred to as patches hereinafter. On the test print sheet onwhich the densities of the background-image and latent-image parts arechanged two-dimensionally, copy-forgery-inhibited patterns from lowerdensities to higher densities are also printed, and a plurality ofpatches having substantially the same densities of the background-imageand latent-image parts are present within a single sheet. Therefore, thedensities of copy-forgery-inhibited patterns can be presented asselectable input values to the user.

In the on-demand copy-forgery-inhibited pattern output method by aprinter described so far, the user can freely select thecopy-forgery-inhibited pattern basic image, camouflage regiondesignation image, and color information. In addition, the densities ofcopy-forgery-inhibited patterns can also be set as input values that canbe selected by the user. If means that allows the user to select thedensity of a copy-forgery-inhibited pattern can be provided, a merit ofincreasing the number of choices can be provided for the user. In orderto improve the user's convenience, a device that allows the user toquickly find out an optimal density of a copy-forgery-inhibited patternimage is required. When the test print sheet on whichcopy-forgery-inhibited pattern images are two-dimensionally laid out bychanging the densities of both the background-image and latent-imageparts is used, the user can quickly find out copy-forgery-inhibitedpattern density parameters (i.e., latent-image and background thresholdpatterns) required to generate a copy-forgery-inhibited pattern imagewhich has the latent-image and background-image parts with substantiallythe same densities, and in which a latent-image can clearly emerge uponcopying. The test print sheet on which copy-forgery-inhibited patternimages are two-dimensionally laid out by changing the densities of boththe background-image and latent-image parts not only allows the user toacquire many kinds of information per sheet, but also has highbrowsability and convenience. Also, since the number of test printsheets to be output when the user finds out an optimalcopy-forgery-inhibited pattern density can be reduced, a paper costreduction can also be achieved.

FIG. 17 shows an example of a test print sheet on which patches aretwo-dimensionally laid out by changing the densities of thebackground-image and latent-image parts. Each patch includes thelatent-image and background-image parts, and may also include acamouflage region. In each patch in FIG. 17, the central portionindicates the latent-image part, and the circumferential portionindicates the background-image part. In the example shown in FIG. 17,the copy-forgery-inhibited pattern basic image used to designate thelatent-image and background-image parts has a rectangular shape.However, the present invention is not limited to the rectangular shape.For example, a character string such as “VOID” or the like may be used.Also, the latent-image and background-image parts may be juxtaposed asindependent patches. Hence, the copy-forgery-inhibited pattern basicimage is not particularly limited as long as copy-forgery-inhibitedpattern images are laid out to be visually recognizable.

On the test print sheet shown in FIG. 17, the density of thelatent-image part is changed in the widthwise direction of a papersheet, and the density of the background-image part is changed in thelongitudinal direction. A patch present at the center of each of patcharrays which are laid out in the longitudinal direction is set to havesubstantially the same densities of the latent-image andbackground-image parts. As a result, even when density variations arepresent due to an environment or deterioration of engine performance,the user can easily find out a patch having the substantially the samedensities of the latent-image and background-image parts.

However, in practice, since density variations are present due to theprinter characteristics and print environment, a patch at the center ofeach of patch arrays which are laid out in the longitudinal directiondoes not always have substantially the same densities of thelatent-image and background-image parts.

The test print sheet is set so that the density of the background-imagepart is darkened in one direction (up direction of the plane of the pagein FIG. 17), and it is lightened in the other direction (down directionof the plane of the page in FIG. 17).

In the example shown in FIG. 17, the density of the background-imagepart of a copy-forgery-inhibited pattern is changed in the longitudinaldirection. As a method of changing the density of the background-imagepart, a method of changing the gray level of an input image signal tothe background-image part dither matrix is available, as describedabove.

For example, when the background dither matrix has a size of 16×16pixels as shown in FIG. 16, the area ratio of black pixels of athreshold pattern changes about 1.5% by changing the gray level of aninput image signal to the background dither matrix by 4.

In this embodiment, a change amount of the gray level of an input imagesignal to the background dither matrix upon changing the density of thebackground-image part in the test printing process is called a “contraststep”, and is used as an index that represents the magnitude of thedensity adjustment unit of the background-image part.

On the other hand, in the example shown in FIG. 17, the density of thelatent-image part is changed in the widthwise direction. As one ofmethods of changing the density of the latent-image part, a method offixing the gray level of an input image signal to the latent-imagedither matrix, and reducing the vertical and horizontal sizes of thelatent-image dither matrix is available.

For example, if a threshold pattern is generated by setting thelatent-image dither matrix size to be 10×10 pixels and the gray level ofan input image signal to be 9, the area ratio of black pixels is 9%; ifa threshold pattern is generated by setting the latent-image dithermatrix size to be 12×12 pixels and the gray level of an input imagesignal to be 9, the area ratio of black pixels is 6.25%; and if athreshold pattern is generated by setting the latent-image dither matrixsize to be 14×14 pixels and the gray level of an input image signal tobe 9, the area ratio of black pixels is about 4.6%.

Therefore, the density of the latent-image part can be changed bychanging the latent-image dither matrix size. When the latent-imagedither matrix sizes are 10×10, 12×12, and 14×14, the numbers of graylevels that can be theoretically expressed are 101 levels (=10×10+1),145 levels (=12×12+1), and 197 levels (=14×14+1).

As another method of changing the density of the latent-image part, amethod of fixing the latent-image dither matrix size, and changing thegray level of an input image signal to the latent-image dither matrix isavailable. For example, if the latent-image dither matrix size is fixedto 10×10, and the gray level of an input image signal is changed to “6”,“9”, and “12”, the area ratios of black pixels are respectively 6%, 9%,and 12%. However, if dots of the latent-image part are as small as theywould disappear after copying, a required condition for the latent-imagepart (i.e., dots remain even after copying) cannot be met. Therefore,the gray level of an input image signal to the latent-image dithermatrix must be set to be equal to or larger than a given level.

As still another method, a latent-image threshold pattern may begenerated by changing both the latent-image dither matrix size and thegray level of an input image signal to the latent-image dither matrix,thereby changing the density.

FIG. 23 is a block diagram showing a copy-forgery-inhibited patterncompositing/printing apparatus comprising the copy-forgery-inhibitedpattern density calibration function. In this arrangement, a selectioninformation input unit 2301 and pattern generation unit 2302 areconnected before the copy-forgery-inhibited patterncompositing/generating apparatus shown in FIG. 1 (2303 in FIG. 23). Theinternal arrangement of the copy-forgery-inhibited patterncompositing/printing apparatus which has the copy-forgery-inhibitedpattern density calibration function will be explained below.

The selection information input unit 2301 inputs information (e.g., anumber printed near a patch) associated with a patch which is determinedto be optimal one as selection information via a user interface. At thistime, a patch of an optimal copy-forgery-inhibited pattern image is theone which has a density of user's choice, and in which thebackground-image and latent-image parts have substantially the samedensities, and the latent-image part remains and the background-imagepart disappears when a test print sheet is copied using a target copyingmachine. When the target copying machine is not available, whether ornot the latent-image part remains and the background-image partdisappears may be checked by copying the test print sheet using anavailable copying machine.

The pattern generation unit 2302 generates patterns required to generatea copy-forgery-inhibited pattern on the basis of the selectioninformation input from the selection information input unit 2301, andinputs them to the next copy-forgery-inhibited patterncompositing/printing apparatus 2303. In case of this embodiment, thepatterns to be generated based on the input selection informationinclude the background and latent-image threshold patterns.

The copy-forgery-inhibited pattern compositing/printing apparatus 2303generates a copy-forgery-inhibited pattern image on the basis of thebackground and latent-image threshold patterns input from the patterngeneration unit 2302 as the previous stage, composites thecopy-forgery-inhibited pattern image to an input document image, andprints out an output document. Since the processes in thecopy-forgery-inhibited pattern compositing/printing apparatus 2303 havealready been described in detail above, a description thereof will beomitted.

According to this embodiment, the copy-forgery-inhibited patterncompositing/printing apparatus which has the copy-forgery-inhibitedpattern density calibration function can be provided.

Even when a patch has equal densities of the background-image andlatent-image parts upon printing, if a test print sheet including suchpatch is copied by the target copying machine, the latent-image part mayremain, but the background-image part may not disappear completely.

However, at this time, a patch whose density of the latent-image part islargely different from that after copying may be determined as anoptimal one. If a latent-image emerges after copying, an effect as thecopy-forgery-inhibited pattern can be provided. In this embodiment, notonly a patch in which the latent-image part remains and thebackground-image part disappears after copying, but also a patch inwhich the density of the background-image part after copying issufficiently lower than that of the latent-image part can be selected asan optimal patch.

FIG. 18 is a flowchart showing the simplest test print sequence.Initially, the test printing process starts in step S1801 in accordancewith an input from a user interface or the like. In step S1802, aprocess for reading setting information from an initial setting filethat saves setting information, or a process for receiving settinginformation input via a user interface is executed. In step S1803,copy-forgery-inhibited pattern density parameters that determine theprint densities of the latent-image and background-image parts upongenerating a copy-forgery-inhibited pattern image are generated on thebasis of the setting information input in step S1802. In thisembodiment, the copy-forgery-inhibited pattern density patterns to begenerated based on the input setting information include background andlatent-image threshold patterns. In step S1804, a test print sheet shownin FIG. 17 is generated on the basis of the copy-forgery-inhibitedpattern density parameters input from step S1803, and is printed out bythe printer.

In step S1805, the user visually compares the densities of thelatent-image and background-image parts of individual patches on thetest print sheet. In visual evaluation, the user selects an optimalpatch in which the latent-image and background-image parts havesubstantially equal densities, and the latent-image part remains and thebackground-image part disappears (or it has a sufficient contrastdifference compared to the latent-image part) upon copying the testprint sheet by a target copying machine using a number associated withthat patch. For example, in the example shown in FIG. 17, patches withdifferent densities are arranged in arrays A, B, and C in the widthwisedirection of a paper sheet, patches having background-image parts withdifferent densities are arranged in the longitudinal direction of thepaper sheet, and values indicating the densities of the background-imageparts are described aside respective patches. Assume that a patch with apreferred density as a copy-forgery-inhibited pattern image is includedin array A, and the value that represents the density of thebackground-image part is 16. In such case, that patch can be selected asA-16.

When the test print function that allows the user to find out an optimalpatch by a single test printing process, as shown in FIG. 17, isimplemented, the test print sheet often includes patches which havesubstantially equal densities of the background-image and latent-imageparts, and in which latent-images are visually inconspicuous. In suchcase, the range of threshold patterns that can set substantially equaldensities of the background-image and latent-image parts must berecognized as initial device density parameters (device profile data) inconsideration of the printer characteristics.

As a practical example of the initial device density parameters,latent-image threshold patterns required to generatecopy-forgery-inhibited pattern images in which latent-image parts havedensities in arrays A, B, and C of a test print sheet, backgroundthreshold patterns which can form background-image parts having printdensities substantially equal to those of arrays A, B, and C (i.e.,contrast zero patterns in respective arrays), density change widths ofbackground-image parts, which are to be changed in the longitudinaldirection of the test print sheet (contrast step parameters inrespective arrays), and the like can be used. The density change rangeof background-image parts (a range of changing background thresholdpatterns in respective ranges; array A in FIG. 17 has a range from 12 to20) can also be used as an initial parameter.

In step S1806, the number (e.g., A-16) associated with the patchselected in step S1805 is input as selection information via a userinterface or the like. In step S1807, copy-forgery-inhibited patterndensity parameters used to determine the print densities of thelatent-image and background-image parts of a copy-forgery-inhibitedpattern image are generated on the basis of the information input instep S1806. More specifically, the copy-forgery-inhibited patterndensity parameters correspond to latent-image and background thresholdpatterns which can form background-image and latent-image parts to havesubstantially equal densities, and allow the background-image part todisappear upon copying. In step S1808, a copy-forgery-inhibited patternimage is generated based on the copy-forgery-inhibited pattern densityparameters generated in step S1807, and is composited to an inputdocument image, thus printing out a composite image. The process in thisstep is the same as that of the copy-forgery-inhibited patterncompositing/printing apparatus described using FIG. 1.

In the test print sequence shown in FIG. 18, if the user cannot find outan optimal patch which has latent-image and background-image parts withsubstantially equal densities from a test print sheet printed by asingle test printing process, density calibration cannot be implemented.However, when the printer suffers a large density variation, or when thehalftone reproduction characteristics of the printer largely depend on amodel or individual, if a large contrast step value is used, an optimalposition at which the densities of the background-image and latent-imageparts become substantially equal to each other cannot often be found bya single process.

FIG. 19 is a flowchart of a test printing process with a reinforceddensity adjustment function compared to the test printing process shownin the flowchart of FIG. 18. A large difference from FIG. 18 is thatthis flowchart has two modes, i.e., coarse and fine test print modes.

Step S1930 shown in FIG. 19 is a step of executing the coarse test printmode, and step S1940 is a step of executing the fine test print mode. Inthe following description, the coarse test print mode as a primary testprinting process will be referred to as “coarse tuning”, and the finetest print mode as a secondary test printing process will be referred toas “fine tuning”.

As internal processes in steps S1930 and S1940, substantially the sameprocesses as those in steps S1804 to S1806 in the simple test printingprocess shown in FIG. 18 are executed.

FIG. 20 shows two different types of sheets used in the test printingprocess, the processing sequence of which is shown in FIG. 19. Referringto FIG. 20, reference numeral 2001 denotes an example of a coarse tuningtest print sheet to be output in step S1904; and 2002, an example of afine tuning test print sheet to be output in step S1908.

Two steps of test printing processes will be described in turn belowusing FIGS. 19 and 20. In the primary test print (coarse tuning) processshown in FIG. 19, a test printing process starts in step S1901 inaccordance with an input from a user interface or the like. In stepS1902, a process for reading setting information from an initial settingfile that saves setting information, or a process for receiving settinginformation input via the user interface is executed.

In step S1903, copy-forgery-inhibited pattern density parameters thatdetermine the print densities of the latent-image and background-imageparts of a copy-forgery-inhibited pattern image are generated on thebasis of the setting information input in step S1902. In thisembodiment, the copy-forgery-inhibited pattern density patterns to begenerated based on the input setting information include background andlatent-image threshold patterns. In step S1904, a coarse tuning testprint sheet 2001 is generated, and is printed out by the printer.

On the coarse tuning test print sheet 2001, the density of thelatent-image part changes in patches which are arranged in the widthwisedirection of a paper sheet, and the density of the background-image partchanges in patches which are arranged in the longitudinal direction, asin FIG. 19. Also, on the coarse tuning test print sheet 2001, backgroundthreshold patterns in patches which are laid out in the longitudinaldirection are generated by changing the gray level of an input imagesignal to the dither matrix in 8-step increments (i.e., contraststep=8).

When the input gray level to the background dither matrix is zero, sinceno dots are printed on the background-image part, such background-imagepart is not suited to a copy-forgery-inhibited pattern image. Therefore,another nonzero value (e.g., 8) may be set for a gray level close tozero. However, when an image for the input gray level=0 to thebackground dither matrix is output, appearance of a latent-image(contrast between the latent-image part and white background) when abackground-image part that disappears completely, i.e., in an idealstate wherein the latent-image emerges after copying, can be confirmedas a merit.

On the coarse tuning test print sheet 2001, since a change in density ofthe background-image part is large between neighboring patches in thelongitudinal direction, it is difficult to precisely adjust thedensities of the background-image part and latent-image part. However,copy-forgery-inhibited pattern density parameters used to generate acopy-forgery-inhibited pattern image which has a background-image partand latent-image part with substantially the same densities can bequickly narrowed down.

Upon generating a threshold pattern using a Bayer dither matrix, whenthe input gray level exceeds a half gray level “128”, the generatedthreshold pattern is expressed by dots which contact each other (not byisolated dots), and an effect of disappearance of the background-imagepart upon copying is hardly obtained. Therefore, for the purpose offinding out an optimal copy-forgery-inhibited pattern image, thebackground-image part suffices to cover the grayscale range of 0 to 128.

Note that the coarse tuning test print sheet 2001 in FIG. 20 shows onlythe grayscale range of 0 to 32 of the background-image part for the sakeof illustrative convenience. However, the coarse tuning test print sheet2001 preferably covers the full grayscale range (0 to 256) expressed bya 16×16 background threshold pattern or the grayscale range (0 to 128)that can be used as the background-image part.

The following description will continue under the assumption that thecoarse tuning test print sheet 2001 substantially covers the grayscalerange from which nearly the same density as that of the latent-imagepart is expected to be obtained (e.g., 0 to 32 in case of the coarsetuning test print sheet 2001).

In order to find out optimal copy-forgery-inhibited pattern densityparameters required to generate a copy-forgery-inhibited pattern imagewhich can approximate the print densities of the latent-image part andbackground-image part using a printer whose halftone reproductioncharacteristics are unknown or a printer which suffers a large densityvariation of the background-image part due to an environment, backgroundthreshold patterns are generated at coarse contrast steps to cover thefull-value range that the background-image part can assume or the valuerange that the background-image part can substantially assume, so as tooutput a test print sheet. In this manner, the range ofcopy-forgery-inhibited pattern density parameters which can setsubstantially the same densities of the background-image part andlatent-image part can be narrowed down without any pre-existingknowledge even using a printer whose halftone reproductioncharacteristics are unknown or a printer which suffers a large densityvariation of the background-image part due to a print environment oraging. Such coarse tuning test print sheet is designed to be generallyapplied to many printers, and is worthful since it does not require anydevice-dependent setups.

In step S1905, the densities of the latent-image and background-imageparts in respective patches on the test print sheet are visuallycompared. In this step, substantially the same process as that describedin step S1805 is executed. However, since the contrast step of thebackground-image part is large, there is a high possibility that thenumber of an optimal patch cannot be found. Therefore, in such case, arange in which an optimal patch is expected to be found is selected.

In this coarse tuning, some methods of designating the range in which anoptimal patch is expected to be found are available. In one method, therange in which an optimal patch is expected to be found is designatedusing a central value. For example, when the third uppermost patch(A-16) has a smallest difference between the densities of thelatent-image and background-image parts in array A on the coarse tuningtest print sheet 2001, the third uppermost patch (A-16) in array A isdesignated as the center where an optimal patch is expected to be found.

In fine tuning to be described later, when the background density ischanged more finely to have the designated patch as the center, there isa high possibility that optimal copy-forgery-inhibited pattern densityparameters required to generate a copy-forgery-inhibited pattern imagewhich has substantially equal densities of the latent-image andbackground-image parts are found.

In another method, a period in which an optimal patch is expected to befound is designated. For example, assume that the third uppermost patch(A-16) in array A on a coarse tuning test print sheet 2001 has abackground-image part lighter than a latent-image part, and the fourthuppermost patch (A-24) has a background-image part darker than alatent-image part. In this case, there is a high possibility that anoptimal patch is found between the third and fourth uppermost patches(A-16) and (A-24) in array A. Therefore, a period in which the magnituderelationship between the densities of the background-image andlatent-image parts changes is designated as a period in which an optimalpatch is expected to be found.

In this case, the user can input the numbers of both the third andfourth uppermost patches (A-16) and (A-24) in array A. However, sincethe method of designating a period by inputting two input values to anoperation menu is often troublesome, the user may calculate anintermediate value between the third and fourth uppermost patches (A-16)and (A-24) and may input the intermediate value (A-20) as the centerwhere an optimal patch is expected to be found.

As in patches in array A, information associated with the center orperiod where an optimal patch is expected to be found is input to arraysB and C, and corresponding patches can be output using a two-dimensionaltest print sheet (e.g., the fine tuning test print sheet 2002).

This fine tuning test print sheet 2002 designates patches (B-8) and(C-8) each of which has the smallest difference between the densities ofthe latent-image and background-image parts in arrays B and C inaddition to array A. In this case, copy-forgery-inhibited patternparameters of different densities can be determined by a single testprinting process.

However, when an optimal patch is to be found by changing the density ofthe background-image part in patches in array A, a test print sheet onwhich the densities of the background-image and latent-image parts arechanged two-dimensionally need not be printed in the fine tuningprocess, and a test print sheet on which only the density of thebackground-image part is changed with respect to the latent-image partwith the designated density need only be output.

In step S1906, the user who executes the test printing process inputsinformation, associated with the center or period where an optimal patchis expected to be found from the test print sheet, via the userinterface on the basis of the visual evaluation result in step S1905.Although not shown in FIG. 19, information previously input in stepS1906 may be saved in a setting file as initial setting information uponexecuting fine tuning step S1940, and that file may be read out.

In step S1907, copy-forgery-inhibited pattern density parametersrequired to generate a copy-forgery-inhibited pattern image which canset substantially equal densities of the background-image andlatent-image parts are generated on the basis of the information inputin step S1906. In this embodiment, a plurality of background thresholdpatterns which are to be printed as the densities within the range inputin step S1906, and a latent-image threshold pattern with the selecteddensity are generated.

In step S1908, a fine tuning test print sheet is generated and printedon the basis of the copy-forgery-inhibited pattern density parametersgenerated in step S1907. For example, on the fine tuning test printsheet 2002 shown in FIG. 20, the gray level of an input image signal tothe background dither matrix is changed more finely to have, as thecenters, the third uppermost patch (A-16) in array A, the seconduppermost patch (B-8) in array B, and the second uppermost patch (C-8)in array C on the coarse tuning test print sheet 2001, which areselected in the coarse tuning process in step S1907, while setting thecontrast step=2. Therefore, patches in which the background-image andlatent-image parts have closer densities compared to the coarse tuningtest print sheet 2001 can be detected.

In this way, in step S1940 that executes fine tuning, a fine tuning testprint sheet which allows the user to find out a patch in which thebackground-image and latent-image parts have closer densities moreaccurately than in step S1930 that executes coarse tuning is generated.In step S1909, the densities of the latent-image and background-imageparts in respective patches on the test print sheet are visuallycompared. In visual evaluation, the user finds out a patch in which thelatent-image and background-image parts have substantially equaldensities, and the latent-image part remains and the background-imagepart disappears (or it has a sufficient contrast difference compared tothe latent-image part) upon copying the test print sheet by a targetcopying machine, and selects the number (e.g., (A-18)) of the optimalpatch from the test print sheet. At this time, if the two-dimensionaltest printing process is done by also changing the density of thelatent-image part, a patch having a preferred density as acopy-forgery-inhibited pattern image can be selected from not only arrayA but also arrays B and C.

In step S1910, the user inputs the number associated with the patchselected in step S1909 as selection information via the user interface.In step S1911, copy-forgery-inhibited pattern density parametersrequired to generate a copy-forgery-inhibited pattern image in which thebackground-image and latent-image parts have approximate print densitiesare generated on the basis of the information input in step S1910. Morespecifically, in this embodiment, latent-image and background thresholdpatterns which can form the background-image and latent-image parts tohave nearly equal densities are generated. In step S1912, acopy-forgery-inhibited pattern image is generated based on thecopy-forgery-inhibited pattern density parameters generated in stepS1911, and is composited to an input document image, thus printing out acomposite image. The process in this step is the same as that in thecopy-forgery-inhibited pattern printing apparatus described using FIG.1.

Note that both the processes in step S1930 that executes coarse tuningand step S1940 that executes fine tuning need not always be executed.For example, only upon installing a printer or making a periodicmaintenance or when a copy-forgery-inhibited pattern image cannot beappropriately output, coarse tuning step S1930 is executed. When acopy-forgery-inhibited pattern is printed routinely, the process in thisstep S1930 may be omitted, and only the process in fine tuning stepS1940 may be executed.

Since coarse tuning is omitted in ordinary use, the time required forcopy-forgery-inhibited pattern density calibration can be reduced. Atthis time, information associated with appropriate parameters as acopy-forgery-inhibited pattern obtained in step S1930 that executescoarse tuning is saved in a setting file. When only fine tuning isexecuted while omitting coarse tuning, the patch output range of thefine tuning test print sheet 2002 can be read out from the saved settingfile, and the fine tuning test print sheet can be generated. In thiscase, it is desirable to design to reduce the number of times of coarsetuning to be re-executed even when a print environment has changed, interms of convenience.

For example, assume that the coarse tuning test print sheet 2001 isprinted, a patch (A-16) in array A has the smallest density differencebetween the latent-image and background-image parts, and a setup fordetailed adjustment in the fine tuning process is made to have (A-16) asthe center. However, assume that an actual printer has suffered adensity variation due to an environment to have a patch (A-20) as thecenter.

If a density variation due to an environment has occurred to have thepatch (A-16) as the center on the fine tuning test print sheet 2002,patches within the range (i.e., A-12 to A-20) of contrast step=4 beforeand after (A-16) can be followed, and the chance of returning to coarsetuning is reduced. However, when a density variation due to anenvironment has occurred to have (A-20) as the center, only patcheswithin the range (i.e., A-12 to A-20) of contrast step=8 in onedirection can be followed on the fine tuning test print sheet 2002, andcoarse tuning must be redone when the density has changed in thedirection of A-24.

In such case, when the user selects the center of fine density change infine tuning from patches on the coarse tuning test print sheet 2001, thecontrast step before and after the center on the coarse tuning testprint sheet 2001 is set to be twice the contrast step before and afterthe center required on the fine tuning test print sheet 2002. With thissetup, since fine tuning can cover the range of neighboring patches tohave the central patch selected from the coarse tuning test print sheet2001, the chance of returning to coarse tuning can be reduced.

In another example, in fine tuning, a relatively large number of patchesmay be set so that not only the range before and after the patchselected as the center in coarse tuning but also the range of severalpatches before and after the center can be covered. In such case, evenwhen a density variation has occurred more or less, the chance ofreturning to coarse tuning can be reduced.

At this time, although not shown, the apparatus or software whichimplements the two-step test print function, the processing sequence ofwhich is shown in FIG. 19, has a step of prompting the user to selectwhether the test printing process starts from coarse tuning or from finetuning on the basis of information obtained by the previously executedcoarse tuning while skipping coarse tuning. If the user selects to startthe test printing process from coarse tuning, the processes shown insteps S1902 to S1912 are executed in turn. If the user selects to startthe test printing process from fine tuning, the saved informationassociated with coarse tuning is read out (corresponding to the processin step S1902), copy-forgery-inhibited pattern parameters are generated(corresponding to the process in step S1903), and the subsequent finetuning processes (steps S1908 to S1912) are executed.

The function of step S1930 that executes coarse tuning may be set as adetailed function (maintenance function) that can be executed by only aservice person who installs or maintains a printer, and may be inhibitedfrom being operated by normal users. For example, software that requestsa password upon executing this step S1930 may be implemented.

Also, when units except for the print unit (printer controller andprinter engine) of the copy-forgery-inhibited patterncompositing/printing apparatus shown in FIG. 1 or 15 are implemented assoftware in a computer, access control may be applied using an accesscontrol function of an OS so that only the administrator of the computercan execute the function of this step S1930.

With the above setups, a trouble that an optimal copy-forgery-inhibitedpattern image cannot be found in only step S1940 of executing finetuning due to a simple setting error or purposeful change by a thirdparty can be avoided.

Furthermore, access control may be applied by similarly requesting apassword or administrator's authority for step S1930 of coarse tuningand step S1940 of fine tuning. Not only a normal user can be preventedfrom falling into a trouble that he or she cannot find an optimalcopy-forgery-inhibited pattern image due to a simple setting error orpurposeful change by a third party, but also, such user can easily printout a document composited with a copy-forgery-inhibited pattern withoutconsidering any copy-forgery-inhibited pattern density calibration.

The fine tuning test print sheet 2002 in FIG. 20 outputs samplesgenerated by changing the densities of both the background-image andlatent-image parts. Alternatively, a desired density of the latent-imagepart may be determined by coarse tuning, and a fine tuning test printsheets that outputs only patches generated by changing the density ofthe background-image part with respect to the determined density of thelatent-image part may be output.

In this case, since the area of patches that can be output increaseswithin a single sheet, a large number of patches may be output per sheetby reducing the contrast step, or patches may be output using thecopy-forgery-inhibited pattern basic image and camouflage regiondesignation image, which are scheduled to be printed after they arecomposited to an actual input document.

On the coarse tuning test print sheet 2001 and fine tuning test printsheet 2002 in FIG. 20, the density and density change width of thebackground-image part may be common to respective arrays or may bedifferent for respective arrays. The coarse tuning test print sheet 2001and fine tuning test print sheet 2002 may adopt quite different layoutsof copy-forgery-inhibited pattern images.

Finally, the processing sequence of a multi-step test printing processthat generalizes the 2-step test print function (coarse tuning and finetuning) will be described.

FIG. 21 is a flowchart showing the processing sequence of a multi-steptest printing process with an advanced function. A test printing processstarts in step S2101 in accordance with an input from a user interfaceor the like. In step S2102, initial setting information required togenerate a copy-forgery-inhibited pattern image is read out. Forexample, the initial setting information is stored in a setting file inan HDD or memory on a computer, and software of the computer reads itout.

In step S2103, copy-forgery-inhibited pattern density parameters thatdetermine the densities of the latent-image and background-image partsof a copy-forgery-inhibited pattern image are generated on the basis ofthe setting information input in step S2102. More specifically, in thisembodiment, latent-image and background threshold patterns that can formthe background-image and latent-image parts to have nearly equaldensities are generated.

In step S2104, a test print sheet is generated and printed based on thecopy-forgery-inhibited pattern density parameters generated in stepS2103. On the test print sheet, patches may be laid out bytwo-dimensionally changing the densities of the background-image andlatent-image parts, or by changing the density of the background-imagepart, as shown in FIG. 17. It is visually evaluated in step S2105 foreach patch on the test print sheet if the background-image andlatent-image parts have nearly equal densities, if the latent-image partremains and the background-image part disappears (or it has a sufficientcontrast difference compared to the latent-image part) in each patch ofthe test print sheet copied by a target copying machine, and so forth.

If it is determined in step S2106 that a patch in which the latent-imageand background-image parts have substantially equal densities, and thelatent-image part remains and the background-image part disappears (orit has a sufficient contrast difference compared to the latent-imagepart) upon copying the test print sheet by a target copying machine isfound from the test print sheet, the flow advances to step S2108.However, if no patch in which the latent-image and background-imageparts have substantially equal densities, and the latent-image partremains and the background-image part disappears (or it has a sufficientContrast difference compared to the latent-image part) upon copying thetest print sheet by a target copying machine is found, the flow advancesto step S2107.

In step S2107, information associated with the center or period where anoptimal patch is expected to be found from the test print sheet is inputvia the user interface using a number or the like associated with thepatch, as has already been described using FIG. 10. At this time, acontrast step as an index used to determine the density change width ofthe background-image part is input together.

As the contrast step, a value smaller than the contrast step used in thealready output test print sheet is preferably set. Note that aspecification that automatically sets the contrast step value bysoftware may be adopted.

In step S2108, copy-forgery-inhibited pattern density parameters used todetermine the print densities of the latent-image and background-imageparts of a copy-forgery-inhibited pattern image are generated on thebasis of the information input in step S2107. The flow returns to stepS2104 to print a test print sheet based on the copy-forgery-inhibitedpattern density parameters generated in step S2108. The flow advances tostep S2105 again to make visual evaluation again. Information associatedwith the center or period where an optimal patch is expected to be foundis re-set until an optimal patch is found, thus repeating the loop.

In step S2109, a number associated with the patch which is selected instep S2105 and in which the latent-image and background-image parts havesubstantially equal densities, and the latent-image part remains and thebackground-image part disappears upon copying the test print sheet by atarget copying machine is input via the user interface or the like. Instep S2110, copy-forgery-inhibited pattern density parameters used todetermine the print densities of the latent-image and background-imageparts of a copy-forgery-inhibited pattern image are generated on thebasis of the information input in step S2109. More specifically, in thisembodiment, latent-image and background threshold patterns which canform the background-image and latent-image parts to have nearly equaldensities and allow the background-image part to disappear upon copyingare generated.

In step S2111, a copy-forgery-inhibited pattern image is generated basedon the copy-forgery-inhibited pattern density parameters generated instep S2110, and is composited to an input document image, thus printingout a composite image. The process in this step is the same as that ofthe copy-forgery-inhibited pattern compositing/printing apparatusdescribed using FIG. 1.

Finally, a modification of the test print sheets shown in FIGS. 17 and20 will be described.

FIG. 24 shows a modification of the test print sheet. On the test printsheets shown in FIGS. 17 and 20, the background-image and latent-imageparts are laid out in one patch. On the test print sheet shown in FIG.24, rectangles (2401, 2403, 2405) of the latent-image part and those(2402, 2403, 2406) of the background-image part are formed, thedensities are fixed inside each rectangle of the latent-image part, andcolumns A, B, and C have different densities.

In each rectangle of the background-image part, the density changessmoothly (to form a gradation from lower to higher densities). Thegradation that forms the interior of each rectangle of thebackground-image part is generated by background threshold patternsbased on a background dither matrix. Beside each rectangle of thebackground-image part, numbers used to identify background thresholdpatterns are assigned. Upon visually designating the densities of thelatent-image and background-image parts, a position where the densitiesbecome nearly equal to each other can be designated by a number (e.g.,(A-16) or the like) as in the test print sheets shown in FIGS. 17 and20.

Using the test print sheet shown in FIG. 24, coarse and fine test printfunctions can be implemented in the same manner as the test print sheetsshown in FIGS. 17 and 20. In the coarse test printing process, agradation range in which the latent-image and background-image parts mayhave nearly equal densities is designated using a number assigned to thebackground-image part. In the fine test printing process, the designatedgradation range is broadened, and the densities of the background-imageand latent-image parts can be compared accurately.

The test print sheet shown in FIG. 24 may be used in place of the coarsetuning test print sheet 2001 shown in FIG. 20. Since the density of thebackground-image part changes continuously, a point where the densitiesof the latent-image and background-image parts become nearly equal toeach other can be finely and easily determined compared to the coarsetuning test print sheet 2001 which coarsely changes the gray level ofthe background-image part. Also, a camouflage pattern may be applied tocolumns A, B, and C, and the densities of the background-image andlatent-image parts can be compared using copy-forgery-inhibited patternimages which are approximate to a copy-forgery-inhibited pattern imageto be finally generated.

Second Embodiment

The second embodiment according to the present invention will bedescribed in detail hereinafter with reference to the accompanyingdrawings. In the second embodiment, respective processes described inthe first embodiment are implemented by a computer.

FIG. 25 is a block diagram showing the basic arrangement of a-computerin the second embodiment. For example, when this computer executes allthe functions except for the print unit (or the printer engine of theprint unit) in FIGS. 1, 15, 22, and 23 in the first embodiment, therespective functions are expressed by a program, which is loaded by thiscomputer, thus implementing all the functions except for the print unit(or the printer engine of the print unit) in FIGS. 1, 15, 22, and 23 inthe first embodiment.

Referring to FIG. 25, reference numeral 2511 denotes a CPU whichcontrols the overall computer, and executes respective processesdescribed in the first embodiment using programs and data stored in aRAM 2512 and ROM 2513. Reference numeral 2512 denotes a RAM which has anarea for temporarily storing programs and data loaded from an externalstorage device 2518 or programs and data downloaded from anothercomputer system 2524 via an I/F (interface) 2523, and also an arearequired for the CPU 2511 to execute various processes.

Reference numeral 2513 denotes a ROM which stores functional programssetting data, and the like of the computer. Reference numeral 2514denotes a display control device which executes a control process fordisplaying images, characters, and the like on a display 2515. Referencenumeral 2515 denotes which displays images, characters, and the like.Note that a CRT, liquid crystal display, and the like can be applied asthe display.

Reference numeral 2516 denotes an operation input device which includesdevices such as a keyboard, mouse, and the like that allow the user toinput various instructions to the CPU 2511. When the user manuallyinputs the camouflage region designation image, copy-forgery-inhibitedpattern basic image, and the like, he or she inputs them via thisoperation input device 2516. Reference numeral 2517 denotes an I/O whichnotifies the CPU 2511 of various instructions and the like input via theoperation input device 2516.

Reference numeral 2518 denotes an external storage device such as a harddisk or the like, which serves as a large-capacity information storagedevice, and stores an OS, a program that makes the CPU 2511 execute theprocesses of the first embodiment, a background dither matrix, alatent-image dither matrix, a generated copy-forgery-inhibited patternimage, an input document image, and the like. Information is writtenin/read out from the external storage device 2518 via an I/O 2519.

Reference numeral 2521 denotes a printer which outputs a document andimage. Output data is sent from the RAM 2512 or external storage device2518 to the printer 2521 via an I/O 2522. As the printer used to outputa document and image, for example, an ink-jet printer, laser beamprinter, thermal transfer printer, dot-impact printer, and the like maybe used.

Reference numeral 2530 denotes a bus used to interconnect the CPU 2511,ROM 2513, RAM 2512, I/O 2522, I/O 2519, display control device 2514, I/F2523, and I/O 2517.

In the second embodiment, the processes of the copy-forgery-inhibitedpattern compositing/printing apparatus or the copy-forgery-inhibitedpattern compositing/printing apparatus with the test print function,except for the print unit, are executed by the computer. Alternatively,processes to be executed by the computer may be executed using adedicated hardware circuit in the printer instead.

Note that the above embodiments present merely examples of the presentinvention, and the technical scope of the present invention must not belimited by such embodiments. That is, the present invention can bepracticed in various forms without departing from its technical scope orits principal features.

Note that the present invention may be applied to either a systemconstituted by a plurality of devices (e.g., a host computer, interfacedevice, reader, printer, and the like), or an apparatus consisting of asingle equipment (e.g., a copying machine, facsimile apparatus, or thelike).

The objects of the present invention are also achieved by supplying arecording medium, which records a program code of a software programthat can implement the functions of the above-mentioned embodiments tothe system or apparatus, and reading out and executing the program codestored in the recording medium by a computer (or a CPU or MPU) of thesystem or apparatus.

In this case, the program code itself read out from the recording mediumimplements the functions of the above-mentioned embodiments, and therecording medium which stores the program code constitutes the presentinvention.

As the recording medium for supplying the program code, for example, afloppy® disk, hard disk, optical disk, magneto-optical disk, CD-ROM,CD-R, magnetic tape, nonvolatile memory card, ROM, and the like may beused.

The functions of the above-mentioned embodiments may be implemented notonly by executing the readout program code by the computer but also bysome or all of actual processing operations executed by an OS (operatingsystem) running on the computer on the basis of an instruction of theprogram code.

Furthermore, the functions of the above-mentioned embodiments may beimplemented by some or all of actual processing operations executed by aCPU or the like arranged in a function extension board or a functionextension unit, which is inserted in or connected to the computer, afterthe program code read out from the recording medium is written in amemory of the extension board or unit.

The present invention has been explained by way of its preferredembodiments. However, the present invention is not limited to theaforementioned embodiments, and various modifications can be made withinthe scope of the appended claims.

CLAIM OF PRIORITY

This application claims priority from Japanese Patent Application No.2003-324690 which was filed on Sep. 17, 2003 and No. 2003-389661 whichwas filed on Nov. 19, 2003, which are hereby incorporated by referenceherein.

1. An image processing apparatus for generating a copy forgery inhibitedpattern image, comprising: a generation unit configured to generate acopy forgery inhibited pattern image by determining a pixel value foreach pixel of the copy forgery inhibited pattern image based on a biggerdot pattern, a smaller dot pattern and a region designation image,wherein the bigger dot pattern is a pattern comprising a predeterminednumber of pixels in which a plurality of pixels having a value of 1 areconcentrated to form a bigger dot, wherein the smaller dot pattern is apattern comprising a predetermined number of pixels in which a pluralityof pixels having a value of 1 are separated from each other by pixelshaving a value of 0, to form scattered smaller dots, wherein the copyforgery inhibited pattern image comprises a plurality of regions, eachregion comprising the same predetermined number of pixels as the biggerdot pattern, and wherein the generation unit prevents the copy forgeryinhibited pattern image from having groups of adjacent dots at aboundary between a bigger dot pattern and a smaller dot pattern, even ifa boundary between a bigger dot area and a smaller dot area in theregion designation image does not coincide with an edge of a bigger dotpattern, by using a pixel value of the region designation image at apixel position corresponding to one predetermined pixel position in eachrespective region of the copy forgery inhibited pattern image todetermine, for every pixel in the respective region, whether to adopt apixel value of a corresponding pixel position in the bigger dot patternor a pixel value of a corresponding pixel position in the smaller dotpattern.
 2. The apparatus according to claim 1, wherein the value of thebigger dot pattern is adopted when the value of the region designationimage at a position corresponding to the predetermined position in therespective region is a first value, and the value of the smaller dotpattern is adopted when the value of the region designation image at aposition corresponding to the predetermined position in the respectiveregion is a second value.
 3. The apparatus according to claim 1, whereinthe predetermined pixel position in each respective region is a pixelposition located at the center of the respective region of the copyforgery inhibited pattern image.
 4. An image processing apparatuscomprising: a generation unit configured to generate an image forcreating printed matter including a region where a density differencebetween the region and neighboring regions on a copy after copying theprinted matter is greater than a density difference on the printedmatter, and the density thickens more than the neighboring regions aftercopying, wherein the generation unit generates an image by determining apixel value for each pixel of the image based on a first pattern fordots included in the region, a second pattern for dots included in theneighboring regions and a region designation image, wherein the firstpattern for dots is a pattern comprising a predetermined number ofpixels in which a plurality of pixels having a value of 1 areconcentrated to form a bigger dot, wherein the second pattern for dotsis a pattern comprising a predetermined number of pixels in which aplurality of pixels having a value of 1 are separated from each other bypixels having a value of 0, to form scattered smaller dots, wherein theimage comprises a plurality of regions, each region comprising the samepredetermined number of pixels as the first pattern for dots, whereinthe generation unit prevents the image from having groups of adjacentdots at a boundary between the first pattern and the second pattern,even if a boundary between a first pattern area and a second patternarea in the region designation image does not coincide with an edge of afirst pattern, by using a pixel value of the region designation image ata pixel position corresponding to one predetermined pixel position ineach respective region of the image to determine, for every pixel in theimage, whether to adopt a pixel value of a corresponding pixel positionin the first pattern or a pixel value of a corresponding pixel positionin the second pattern.
 5. The apparatus according to claim 4, whereinthe value of the first pattern is adopted when the value of the regiondesignation image at the position corresponding to the predeterminedposition in the respective region is a first value, and the value of thesecond pattern is adopted as when the value of the region designationimage at the position corresponding to the predetermined position in therespective region is a second value.
 6. The apparatus according to claim4, wherein the first pattern differs from the second pattern in the sizeof the pattern.
 7. A method in an image processing apparatus forgenerating a copy forgery inhibited pattern image, the methodcomprising: generating a copy forgery inhibited pattern image bydetermining a pixel value for each pixel of the copy forgery inhibitedpattern image based on a bigger dot pattern, a smaller dot pattern and aregion designation image, wherein the bigger dot pattern is a patterncomprising a predetermined number of pixels in which a plurality ofpixels having a value of 1 are concentrated to form a bigger dot,wherein the smaller dot pattern is a pattern comprising a predeterminednumber of pixels in which a plurality of pixels having a value of 1 areseparated from each other by pixels having a value of 0, to formscattered smaller dots, wherein the copy forgery inhibited pattern imagecomprises a plurality of regions, each region comprising the samepredetermined number of pixels as the bigger dot pattern, wherein, thegenerating step prevents the copy forgery inhibited pattern image fromhaving groups of adjacent dots at a boundary between a bigger dotpattern and a smaller dot pattern, even if a boundary between a biggerdot area and a smaller dot area in the region designation image does notcoincide with an edge of a bigger dot pattern, by using a pixel value ofthe region designation image at a pixel position corresponding to onepredetermined pixel position in each respective region of the copyforgery inhibited pattern image to determine, for every pixel in therespective region, whether to adopt a pixel value of a correspondingpixel position in the bigger dot pattern or a pixel value of acorresponding pixel position in the smaller dot pattern, and wherein thegenerating step is implemented by a CPU.
 8. The method according toclaim 7, wherein the value of the bigger dot pattern is adopted when thevalue of the region designation image at the position corresponding tothe predetermined position in the respective region is a first value,and the value of the smaller dot pattern is adopted designation image atthe position corresponding to the predetermined position in therespective region is a second value.
 9. The method according to claim 7,wherein the predetermined pixel position in each respective region ofthe copy forgery inhibited pattern image is a pixel position located atthe center of the respective region.
 10. A method in an image processingapparatus, the method comprising: generating an image for creatingprinted matter including a region where a density difference between theregion and neighboring regions on a copy after copying the printedmatter is greater than a density difference on the printed matter, andthe density thickens more than the neighboring regions after copying,wherein, in the generating step, an image is generated by determining apixel value for each pixel of the image based on a first pattern fordots included in the region, a second pattern for dots included in theneighboring regions and a region designation image, wherein the firstpattern for dots is a pattern comprising a predetermined number ofpixels in which a plurality of pixels having a value of 1 areconcentrated to form a bigger dot, wherein the second pattern for dotsis a pattern comprising a predetermined number of pixels in which aplurality of pixels having a value of 1 are separated from each other bypixels having a value of 0, to form scattered smaller dots, wherein theimage comprises a plurality of regions, each region comprising the samepredetermined number of pixels as the first pattern for dots, whereinthe generating step prevents the image from having groups of adjacentdots at a boundary between the first pattern and the second pattern,even if a boundary between a first pattern area and a second patternarea in the region designation image does not coincide with an edge of afirst pattern, by using a pixel value of the region designation image ata pixel position corresponding to one predetermined pixel position ineach respective region of the image to determine, for every pixel in theimage, whether to adopt a pixel value of a corresponding pixel positionin the first pattern or a pixel value of a corresponding pixel positionin the second pattern, and wherein the generating step is implemented bya CPU.
 11. The method according to claim 10, wherein the value of thefirst pattern is adopted when the value of the region designation imageat the position corresponding to the predetermined position in theregion is a first value, and the value of the second pattern is adoptedwhen the value of the region designation image at the positioncorresponding to the predetermined position in the respective region isa second value.
 12. The method according to claim 10, wherein the firstpattern differs from the second pattern in the size of the pattern. 13.A non-transitory computer-readable recording medium in which is encodeda program for causing a computer to execute the method recited in claim7.
 14. A non-transitory computer-readable recording medium in which isencoded a program for causing a computer to execute the method recitedin claim
 10. 15. An image processing apparatus for generating a copyforgery inhibited pattern image, comprising: a generation unitconfigured to generate a copy forgery inhibited pattern image bydetermining a pixel value for each pixel of the copy forgery inhibitedpattern image based on a bigger dot pattern, a smaller dot pattern and aregion designation image, wherein the bigger dot pattern is a patterncomprising a predetermined number of pixels in which a plurality ofpixels having a value of 1 are concentrated to form a bigger dot,wherein the smaller dot pattern is a pattern comprising a predeterminednumber of pixels in which a plurality of pixels having a value of 1 areseparated from each other by pixels having a value of 0, to formscattered smaller dots, wherein the copy forgery inhibited pattern imagecomprises a plurality of regions, each region comprising the samepredetermined number of pixels as the bigger dot pattern, and whereinthe generation unit ensures that each bigger dot pattern in the copyforgery inhibited pattern image, other than a bigger dot pattern formedat the edge of the copy forgery inhibited pattern image, is formed witha white background by, for each region of the copy forgery inhibitedpattern image, reading only a pixel value of the region designationimage at a pixel position corresponding to one predetermined pixelposition in the respective region of the copy forgery inhibited patternimage, and using values identical to the read value to determine, forevery pixel in the respective region, whether to adopt a pixel value ofa corresponding pixel position in the bigger dot pattern or a pixelvalue of a corresponding pixel position in the smaller dot pattern.